Iron-Catalyzed Cross-Coupling of α-Allenyl Esters with Grignard Reagents for the Synthesis of 1,3-Dienes

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This article references 16 other publications.

1. 1

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   A review. Fungal infections represent a serious problem for patients with immune systems compromised either by HIV infection, or administration of immunosuppressive drugs during cancer therapy and organ transplantation. High dissemination and proliferation rates of many pathogenic fungi along with their insusceptibility to common antimicrobial drugs urge implementation of efficient and reliable antifungal therapy. Up to date, polyene macrolide antibiotics proved to be the most effective antifungal agents due to their potent fungicidal activity, broad spectrum, and relatively low frequency of resistance among the fungal pathogens. However, polyene macrolides are rather toxic, causing such serious side effects as renal failure, hypokalemia and thrombophlebitis, esp. upon i.v. administration. Current views on the biosynthesis of polyene macrolides, their mode of action and structure-function relationship, as well as strategies used to overcome the toxicity problem are discussed in this review. In addn., some of the new potential applications for polyene macrolides in therapy of prion diseases, HIV infection and cancer are highlighted.

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   Chemical Reviews (Washington, D. C.) (1995), 95 (6), 2021-40CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

   Oxo polyene macrolide antibiotics are reviewed with 76 refs.

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2. 2

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   The Diels-Alder reaction in total synthesis

   Nicolaou, K. C.; Snyder, Scott A.; Montagnon, Tamsyn; Vassilikogiannakis, Georgios

   Angewandte Chemie, International Edition (2002), 41 (10), 1668-1698CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH)

   A review. The Diels-Alder reaction has both enabled and shaped the art and science of total synthesis over the last few decades to an extent which, arguably, has yet to be eclipsed by any other transformation in the current synthetic repertoire. With myriad applications of this magnificent pericyclic reaction, often as a crucial element in elegant and programmed cascade sequences facilitating complex mol. construction, the Diels-Alder cycloaddn. has afforded numerous and unparalleled solns. to a diverse range of synthetic puzzles provided by nature as natural products. In celebration of the 100th anniversary of Alder's birth, selected examples of the awesome power of the reaction he helped to discover are discussed in this review in the context of total synthesis to illustrate its overall versatility and underscore its vast potential which has yet to be fully realized.

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   Catalytic enantioselective Diels-Alder reactions: Methods, mechanistic fundamentals, pathways, and applications

   Corey, E. J.

   Angewandte Chemie, International Edition (2002), 41 (10), 1650-1667CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH)

   A review. One hundred years after the birth of Kurt Alder and seventy-five years after the discovery of his famous reaction, one of the most important and fascinating transformations in chem., research on that process continues to surprise, excite, delight, and inform the chem. community. This article is based on presentations given first at the University of Cologne, Germany (Kurt Alder lecture, 1992), then at the Roger Adams Award Symposium (1993), and later at the Burgenstock Conference of 2001, and describes research by our group on the development and understanding of enantioselective versions of the Diels - Alder reactions. The elements of this review include (1) development of new chiral Lewis acid catalysts for highly enantioselective (>25:1) [4+2] cycloaddns.; (2) the fine mechanistic details and pre-transition-state assemblies of these reactions; (3) the fundamental understanding of catalytic activity and enantioselectivity for highly enantioselective Diels-Alder processes; and (4) applications to the synthesis of complex mols. The range and power of the Diels-Alder reaction have steadily increased over seven decades. The end of this remarkable development is not in sight, a high compliment to this field of Science and to its great inventor.

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3. 3

   (a) Li, M.-M.; Cheng, L.; Xiao, L.-J.; Xie, J.-H.; Zhou, Q.-L. Palladium-Catalyzed Asymmetric Hydrosulfonylation of 1,3-Dienes with Sulfonyl Hydrazides. Angew. Chem., Int. Ed. 2021, 60, 2948– 2951,  DOI: 10.1002/anie.202012485

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   Palladium-Catalyzed Asymmetric Hydrosulfonylation of 1,3-Dienes with Sulfonyl Hydrazides

   Li, Ming-Ming; Cheng, Lei; Xiao, Li-Jun; Xie, Jian-Hua; Zhou, Qi-Lin

   Angewandte Chemie, International Edition (2021), 60 (6), 2948-2951CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

   A highly enantio- and regioselective hydrosulfonylation of 1,3-dienes with sulfonyl hydrazides has been realized by using a palladium catalyst contg. a monodentate chiral spiro phosphoramidite ligand [e.g., E/Z-1-phenyl-1,3-butadiene + TsNHNH2 → I (92%, 93% ee)]. The reaction provided an efficient approach to synthetically useful chiral allylic sulfones. Mechanistic studies suggest that the reaction proceeds through the formation of an allyl hydrazine intermediate and subsequent rearrangement to the chiral allylic sulfone product. The transformation of the allyl hydrazine intermediate to the product is the enantioselectivity-detg. step.

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   (b) Perry, G. J. P.; Jia, T.; Procter, D. J. Copper-Catalyzed Functionalization of 1,3-Dienes: Hydrofunctionalization, Borofunctionalization, and Difunctionalization. ACS Catal. 2020, 10, 1485– 1499,  DOI: 10.1021/acscatal.9b04767

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   Copper-Catalyzed Functionalization of 1,3-Dienes: Hydrofunctionalization, Borofunctionalization, and Difunctionalization

   Perry, Gregory J. P.; Jia, Tao; Procter, David J.

   ACS Catalysis (2020), 10 (2), 1485-1499CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

   A review. The catalytic conversion of chem. feedstocks into products of medicinal and agricultural value is a key theme across modern synthetic chem. As 1,3-dienes are readily available from industrial cracking processes, there is great interest in the development of sustainable methods for the functionalization of these simple mols. Although initial developments in this field have required precious-transition-metal catalysts, there has been a push toward the use of inexpensive, nontoxic, and more abundant copper catalysts to promote functionalization. This Perspective covers the many developments in the area of copper-catalyzed functionalization of 1,3-dienes, in particular hydrofunctionalization, borofunctionalization, and difunctionalization (e.g., diamination).

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   (c) Cheng, L.; Li, M.-M.; Xiao, L.-J.; Xie, J.-H.; Zhou, Q.-L. Nickel(0)-Catalyzed Hydroalkylation of 1,3-Dienes with Simple Ketones. J. Am. Chem. Soc. 2018, 140, 11627– 11630,  DOI: 10.1021/jacs.8b09346

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   Nickel(0)-Catalyzed Hydroalkylation of 1,3-Dienes with Simple Ketones

   Cheng, Lei; Li, Ming-Ming; Xiao, Li-Jun; Xie, Jian-Hua; Zhou, Qi-Lin

   Journal of the American Chemical Society (2018), 140 (37), 11627-11630CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   We developed a highly regioselective addn. of 1,3-dienes with simple ketones by nickel-hydride catalyst bearing DTBM-SegPhos ligand. A wide range of arom. and aliph. ketones directly coupled with 1,3-dienes, providing synthetically useful γ,δ-unsatd. ketones in high yield and regioselectivity. The asym. version of the reaction was also realized in high enantioselectivity by using novel chiral ligand DTBM-HO-BIPHEP. The utility of this hydroalkylation was demonstrated by facile product modification and enantioselective synthesis of (R)-flobufen.

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   A review. This review examines recent developments in late transition metal-catalyzed hydroamination and -amidation reactions. In this review, usage of the term hydroamidation is not limited to the substrate classes of amides, sulfonamides, and phosphonamides, but extended to structurally related compds. with a similar pKa range and reactivity, such as carbamates, lactams, ureas, amidines, guanidines, etc.

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4. 4

   (a) Xiong, Y.; Sun, Y.; Zhang, G. Recent Advances on Catalytic Asymmetric Difunctionalization of 1,3-Dienes. Tetrahedron Lett. 2018, 59, 347– 355,  DOI: 10.1016/j.tetlet.2017.12.059

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   Xiong, Yang; Sun, Youwen; Zhang, Guozhu

   Tetrahedron Letters (2018), 59 (4), 347-355CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)

   A review. This review mainly focuses on recent advances in catalytic activation of 1,3-dienes by transition-metals followed by asym. addn.

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   (b) McNeill, E.; Ritter, T. 1,4-Functionalization of 1,3-Dienes With Low-Valent Iron Catalysts. Acc. Chem. Res. 2015, 48, 2330– 2343,  DOI: 10.1021/acs.accounts.5b00050

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   A review discusses the work of the Ritter group in the development of iminopyridine-ligated reduced iron catalysts for the regio- and diastereoselective functionalization of 1,3-dienes, including hydrovinylation, hydroboration, hydrosilylation, and polymn. of 1,3-dienes, including the development of a convenient low-valent iron complex precursor under homogeneous conditions and kinetics and mechanistic studies of the reactions.

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5. 5

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   The Wittig olefination reaction and modifications involving phosphoryl-stabilized carbanions. Stereochemistry, mechanism, and selected synthetic aspects

   Maryanoff, Bruce E.; Reitz, Allen B.

   Chemical Reviews (Washington, DC, United States) (1989), 89 (4), 863-927CODEN: CHREAY; ISSN:0009-2665.

   A review with 558 refs. on Wittig olefination of aldehydes and ketones, with emphasis on information added to this topic from 1978 to the present.

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6. 6

   (a) Hou, C.-J.; Schuppe, A. W.; Knippel, J. L.; Ni, A. Z.; Buchwald, S. L. A Dual CuH- and Pd-Catalyzed Stereoselective Synthesis of Highly Substituted 1,3-Dienes. Org. Lett. 2021, 23, 8816– 8821,  DOI: 10.1021/acs.orglett.1c03324

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   6a

   A Dual CuH- and Pd-Catalyzed Stereoselective Synthesis of Highly Substituted 1,3-Dienes

   Hou, Chuan-Jin; Schuppe, Alexander W.; Knippel, James Levi; Ni, Anton Z.; Buchwald, Stephen L.

   Organic Letters (2021), 23 (22), 8816-8821CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)

   A method for the stereoselective hydroalkenylation of alkynes ArCCR (Ar = Ph, thiophen-2-yl, 6-methoxypyridin-3-yl, etc.; R = n-Bu, CHO, Ph, etc.), utilizing readily available enol triflates e.g., I was reported. In situ-generated and geometrically pure vinyl-Cu(I) species to form the Z,Z- or Z,E-1,3-dienes in excellent stereoselectivity and yield were leveraged. This approach allowed for the synthesis of highly substituted Z-dienes, including pentasubstituted 1,3-dienes e.g., II, which are difficult to prep. by existing approaches.

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   (b) Soengas, R. G.; Rodríguez-Solla, H. Modern Synthetic Methods for the Stereoselective Construction of 1,3-Dienes. Molecules 2021, 26, 249,  DOI: 10.3390/molecules26020249

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   Modern synthetic methods for the stereoselective construction of 1,3-dienes

   Soengas, Raquel G.; Rodriguez-Solla, Humberto

   Molecules (2021), 26 (2), 249CODEN: MOLEFW; ISSN:1420-3049. (MDPI AG)

   A review. The 1,3-butadiene motif is widely found in many natural products and drug candidates with relevant biol. activities. Moreover, dienes are important targets for synthetic chemists, due to their ability to give access to a wide range of functional group transformations, including a broad range of C-C bond-forming processes. Therefore, the stereoselective prepn. of dienes have attracted much attention over the past decades, and the search for new synthetic protocols continues unabated. The aim of this review is to give an overview of the diverse methodologies that have emerged in the last decade, with a focus on the synthetic processes that meet the requirements of efficiency and sustainability of modern org. chem.

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   (c) Nguyen, V. T.; Dang, H. T.; Pham, H. H.; Nguyen, V. D.; Flores-Hansen, C.; Arman, H. D.; Larionov, O. V. Highly Regio- and Stereoselective Catalytic Synthesis of Conjugated Dienes and Polyenes. J. Am. Chem. Soc. 2018, 140, 8434– 8438,  DOI: 10.1021/jacs.8b05421

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   6c

   Highly Regio- and Stereoselective Catalytic Synthesis of Conjugated Dienes and Polyenes

   Nguyen, Vu T.; Dang, Hang T.; Pham, Hoang H.; Nguyen, Viet D.; Flores-Hansen, Carsten; Arman, Hadi D.; Larionov, Oleg V.

   Journal of the American Chemical Society (2018), 140 (27), 8434-8438CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   Aryl- and alkenyl-substituted 1,3-dienes were prepd. by regioselective and stereoselective ring opening and coupling reactions of sulfolenes (2,5-dihydrothiophene-1,1-dioxides) with aryl bromides and chlorides and alkenyl bromides in the presence of Pd(OAc)2, 1,2-bis(diphenylphosphino)benzene, either KOMe or KOt-Bu, and K2CO3 in THF. Coupling reactions of sulfolene with aryl bromides such as RBr (R = 4-NCC6H4, 4-AcNHC6H4, Ph, 4-F3CC6H4, 4-ClC6H4, 3-MeSC6H4, 3-F3CC6H4, 2-NCC6H4, 1-naphthyl, 5-H2N-1-naphthyl, 4-F-1-naphthyl, 9-phenanthrenyl) or aryl chlorides or alkenyl bromides yielded (E)-1,3-dienes such as (E)-RCH:CHCH:CH2 (R = 4-NCC6H4, 4-AcNHC6H4, Ph, 4-F3CC6H4, 4-ClC6H4, 3-MeSC6H4, 3-F3CC6H4, 2-NCC6H4, 1-naphthyl, 5-H2N-1-naphthyl, 4-F-1-naphthyl, 9-phenanthrenyl). Coupling reactions of aryl or alkenyl bromides 2-substituted sulfolenes or of 3,4-dimethylsulfolene yielded (E,E)-1,4-disubstituted or (E)-2,3-dimethyl-1,3-dienes; coupling reactions of 3-substituted sulfolenes or of 2,2,4-trimethylsulfolene yielded (Z)-1,3-dienes.

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   (d) Liu, M.; Yang, P.; Karunananda, M. K.; Wang, Y.; Liu, P.; Engle, K. M. C(alkenyl)–H Activation via Six-Membered Palladacycles: Catalytic 1,3-Diene Synthesis. J. Am. Chem. Soc. 2018, 140, 5805– 5813,  DOI: 10.1021/jacs.8b02124

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   6d

   C(alkenyl)-H Activation via Six-Membered Palladacycles: Catalytic 1,3-Diene Synthesis

   Liu, Mingyu; Yang, Pusu; Karunananda, Malkanthi K.; Wang, Yanyan; Liu, Peng; Engle, Keary M.

   Journal of the American Chemical Society (2018), 140 (17), 5805-5813CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   A catalytic method to prep. highly substituted 1,3-dienes from two different alkenes is described using a directed, palladium(II)-mediated C(alkenyl)-H activation strategy. The transformation exhibits broad scope across three synthetically useful substrate classes masked with suitable bidentate auxiliaries (4-pentenoic acids, allylic alcs., and bishomoallylic amines) and tolerates internal nonconjugated alkenes, which have traditionally been a challenging class of substrates in this type of chem. Catalytic turnover is enabled by either MnO2 as the stoichiometric oxidant or co-catalytic Co(OAc)2 and O2 (1 atm). Exptl. and computational studies were performed to elucidate the preference for C(alkenyl)-H activation over other potential pathways. As part of this effort, a structurally unique alkenylpalladium(II) dimer was isolated and characterized.

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   (e) Olivares, A. M.; Weix, D. J. Multimetallic Ni- and Pd-Catalyzed Cross-Electrophile Coupling To Form Highly Substituted 1,3-Dienes. J. Am. Chem. Soc. 2018, 140, 2446– 2449,  DOI: 10.1021/jacs.7b13601

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   6e

   Multimetallic Ni- and Pd-Catalyzed Cross-Electrophile Coupling To Form Highly Substituted 1,3-Dienes

   Olivares, Astrid M.; Weix, Daniel J.

   Journal of the American Chemical Society (2018), 140 (7), 2446-2449CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   The synthesis of highly substituted 1,3-dienes from the coupling of vinyl bromides with vinyl triflates is reported for the first time. The coupling is catalyzed by a combination of (5,5'-bis(trifluoromethyl)-2,2'-bipyridine)NiBr2 and (1,3-bis(diphenylphosphino)propane)PdCl2 in the presence of a zinc reductant. This method affords tetra- and penta-substituted 1,3-dienes that would otherwise be difficult to access and tolerates electron-rich and -poor substituents, heterocycles, an aryl bromide, and a pinacol boronate ester. Mechanistically, the reaction appears to proceed by an unusual zinc-mediated transfer of a vinyl group between the nickel and palladium centers.

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   (f) Hu, X.-H.; Zhang, J.; Yang, X.-F.; Xu, Y.-H.; Loh, T.-P. Stereo- and Chemoselective Cross-Coupling between Two Electron-Deficient Acrylates: An Efficient Route to (Z,E)-Muconate Derivatives. J. Am. Chem. Soc. 2015, 137, 3169– 3172,  DOI: 10.1021/ja512237d

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   6f

   Stereo- and Chemoselective Cross-Coupling between Two Electron-Deficient Acrylates: An Efficient Route to (Z,E)-Muconate Derivatives

   Hu, Xu-Hong; Zhang, Jian; Yang, Xiao-Fei; Xu, Yun-He; Loh, Teck-Peng

   Journal of the American Chemical Society (2015), 137 (9), 3169-3172CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   A Ru-catalyzed direct oxidative cross-coupling reaction of acrylates was developed. It offers a straightforward and atom-economical protocol for the synthesis of functionalized (Z,E)-muconate derivs. in moderate to good yields with good stereo- and chemoselectivities [e.g., Bu methacrylate + Bu acrylate → I (48%, 92/8 Z,E/E,E)]. The conjugated muconates bearing differentiable terminal functionality can be selectively transformed into versatile synthetic intermediates widely used in org. synthesis.

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   (g) Delcamp, J. H.; Gormisky, P. E.; White, M. C. Oxidative Heck Vinylation for the Synthesis of Complex Dienes and Polyenes. J. Am. Chem. Soc. 2013, 135, 8460– 8463,  DOI: 10.1021/ja402891m

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   6g

   Oxidative Heck Vinylation for the Synthesis of Complex Dienes and Polyenes

   Delcamp, Jared H.; Gormisky, Paul E.; White, M. Christina

   Journal of the American Chemical Society (2013), 135 (23), 8460-8463CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   An oxidative Heck reaction for selective complex diene and polyene formation is presented. The reaction proceeds via oxidative Pd(II)/sulfoxide catalysis (White catalyst) that retards palladium-hydride isomerizations which previously limited the Heck manifold's capacity for furnishing stereodefined conjugated dienes. Limiting quantities of nonactivated terminal olefins (1 equiv) and slight excesses of vinyl boronic esters (1.5 equiv) that feature diverse functionality can be used to furnish complex dienes and polyenes in good yields and excellent selectivities (generally E:Z = >20:1; internal:terminal = >20:1). Because this reaction only requires prior activation of a single vinylic carbon, improvements in efficiency are obsd. for synthetic sequences relative to ones featuring reactions that require activation of both coupling partners. This methodol. was successfully applied to the synthesis of the maclolactin A C12-C24 segment I and of the amphidinolide C C17-C29 segment.

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   (h) Zheng, C.; Wang, D.; Stahl, S. S. Catalyst-Controlled Regioselectivity in the Synthesis of Branched Conjugated Dienes via Aerobic Oxidative Heck Reactions. J. Am. Chem. Soc. 2012, 134, 16496– 16499,  DOI: 10.1021/ja307371w

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   6h

   Catalyst-Controlled Regioselectivity in the Synthesis of Branched Conjugated Dienes via Aerobic Oxidative Heck Reactions

   Zheng, Changwu; Wang, Dian; Stahl, Shannon S.

   Journal of the American Chemical Society (2012), 134 (40), 16496-16499CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   Pd-catalyzed aerobic oxidative coupling of vinylboronic acids and electronically unbiased alkyl olefins provides regioselective access to 1,3-disubstituted conjugated dienes. Catalyst-controlled regioselectivity is achieved by using 2,9-dimethylphenanthroline as a ligand. The obsd. regioselectivity is opposite to that obsd. from a traditional (nonoxidative) Heck reaction between a vinyl bromide and an alkene. DFT computational studies reveal that steric effects of the 2,9-dimethylphenanthroline ligand promote C-C bond formation at the internal position of the alkene.

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   (i) Stang, E. M.; White, M. C. Molecular Complexity via C–H Activation: A Dehydrogenative Diels–Alder Reaction. J. Am. Chem. Soc. 2011, 133, 14892– 14895,  DOI: 10.1021/ja2059704

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   6i

   Molecular Complexity via C-H Activation: A Dehydrogenative Diels-Alder Reaction

   Stang, Erik M.; White, M. Christina

   Journal of the American Chemical Society (2011), 133 (38), 14892-14895CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   Traditionally, C-H oxidn. reactions install oxidized functionality onto a preformed mol. skeleton, resulting in a local mol. change. The use of C-H activation chem. to construct complex mol. scaffolds is a new area with tremendous potential in synthesis. Herein is reported a Pd(II)/bis-sulfoxide-catalyzed dehydrogenative Diels-Alder reaction that converts simple terminal olefins into complex cycloadducts in a single operation.

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   (j) Hansen, A. L.; Ebran, J.-P.; Ahlquist, M.; Norrby, P.-O.; Skrydstrup, T. Heck Coupling with Nonactivated Alkenyl Tosylates and Phosphates: Examples of Effective 1,2-Migrations of the Alkenyl Palladium(II) Intermediates. Angew. Chem., Int. Ed. 2006, 45, 3349– 3353,  DOI: 10.1002/anie.200600442

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   6j

   Heck coupling with nonactivated alkenyl tosylates and phosphates: examples of effective 1,2-migrations of the alkenyl palladium(II) intermediates

   Hansen, Anders L.; Ebran, Jean-Philippe; Ahlquist, Maarten; Norrby, Per-Ola; Skrydstrup, Troels

   Angewandte Chemie, International Edition (2006), 45 (20), 3349-3353CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

   A catalytic system composed of a palladium complex with a basic, hindered alkyl phosphine ligand is capable of promoting Heck coupling of nonactivated vinyl tosylates and phosphates with electron-deficient olefins. An unexpected 1,2-migration of the alkenyl PdII intermediates leads to the isomerized Heck coupling product.

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   (k) Molander, G. A.; Felix, L. A. Stereoselective Suzuki–Miyaura Cross-Coupling Reactions of Potassium Alkenyltrifluoroborates with Alkenyl Bromides. J. Org. Chem. 2005, 70, 3950– 3956,  DOI: 10.1021/jo050286w

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   6k

   Stereoselective Suzuki-Miyaura cross-coupling reactions of potassium alkenyltrifluoroborates with alkenyl bromides

   Molander, Gary A.; Felix, Luciana A.

   Journal of Organic Chemistry (2005), 70 (10), 3950-3956CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)

   The stereoselective synthesis of conjugated dienes using air-stable potassium alkenyltrifluoroborates as coupling partners is described. The palladium-catalyzed cross-coupling reaction of potassium (E)- and (Z)-alkenyltrifluoroborates with either (E)- or (Z)-alkenyl bromides proceeded readily with moderate to excellent yields to give the corresponding (E,E)-, (E,Z)-, (Z,E)-, or (Z,Z)-conjugated dienes stereospecifically. The cross-coupling can generally be effected using a catalytic amt. of Pd(OAc)2 and PPh3, and an excess of Cs2CO3 in THF-H2O. A variety of functional groups were tolerated in both coupling partners.

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7. 7

   (a) Huang, Q.; Su, Y.-X.; Sun, W.; Hu, M.-Y.; Wang, W.-N.; Zhu, S.-F. Iron-Catalyzed Vinylzincation of Terminal Alkynes. J. Am. Chem. Soc. 2022, 144, 515– 526,  DOI: 10.1021/jacs.1c11072

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   7a

   Iron-Catalyzed Vinylzincation of Terminal Alkynes

   Huang, Qiang; Su, Yu-Xuan; Sun, Wei; Hu, Meng-Yang; Wang, Wei-Na; Zhu, Shou-Fei

   Journal of the American Chemical Society (2022), 144 (1), 515-526CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   Organozinc reagents are among the most commonly used organometallic reagents in modern synthetic chem., and multifunctionalized organozinc reagents can be synthesized from structurally simple, readily available ones by alkyne carbozincation. However, this method suffers from poor tolerance for terminal alkynes, and transformation of the newly introduced org. groups is difficult, which limits its applications. Herein, the authors report a method for vinylzincation of terminal alkynes catalyzed by newly developed Fe catalysts bearing 1,10-phenanthroline-imine ligands. This method provides efficient access to novel organozinc reagents with a diverse array of structures and functional groups from readily available vinylzinc reagents and terminal alkynes. The method features excellent functional group tolerance (tolerated functional groups include amino, amide, cyano, ester, hydroxyl, sulfonyl, acetal, phosphono, pyridyl), a good substrate scope (suitable terminal alkynes include aryl, alkenyl, and alkyl acetylenes bearing various functional groups), and high chemoselectivity, regioselectivity, and stereoselectivity. The method could significantly improve the synthetic efficiency of various important bioactive mols., including vitamin A. Mechanistic studies indicate that the new Fe-1,10-phenanthroline-imine catalysts developed in this study has an extremely crowded reaction pocket, which promotes efficient transfer of the vinyl group to the alkynes, disfavors substitution reactions between the Zn reagent and the terminal C-H bond of the alkynes, and prevents the further reactions of the products. The authors' findings show that Fe catalysts can be superior to other metal catalysts in terms of activity, chemoselectivity, regioselectivity, and stereoselectivity when suitable ligands were used.

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   (b) Guo, Z.; Wen, H.; Liu, G.; Huang, Z. Iron-Catalyzed Regio- and Stereoselective Hydrosilylation of 1,3-Enynes To Access 1,3-Dienylsilanes. Org. Lett. 2021, 23, 2375– 2379,  DOI: 10.1021/acs.orglett.1c00670

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   7b

   Iron-Catalyzed Regio- and Stereoselective Hydrosilylation of 1,3-Enynes To Access 1,3-Dienylsilanes

   Guo, Zhihao; Wen, Huanan; Liu, Guixia; Huang, Zheng

   Organic Letters (2021), 23 (6), 2375-2379CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)

   A regio- and stereoselective hydrosilylation of 1,3-enynes with primary and secondary silanes to access 1,3-dienylsilanes is accomplished by employing an iron precatalyst bearing iminopyridine-oxazoline (IPO) ligand. The hydrosilylation proceeds via syn-addn. of a Si-H bond to the alkyne group of 1,3-enynes, incorporating the silyl group at the site proximal to the alkene. The reaction features mild conditions, broad substrate scope, and good functional group tolerance. The synthetic utility was demonstrated by gram-scale reactions and further transformations.

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8. 8

   (a) Xu, G.-L.; Duan, Y.-T.; Wang, Z.-X. Copper-Catalyzed Reaction of 2,3-Allenols with Silylzinc Reagents: Access to 2-Silyl-1,3-butadienes. Org. Lett. 2022, 24, 7934– 7938,  DOI: 10.1021/acs.orglett.2c03041

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   8a

   Copper-Catalyzed Reaction of 2,3-Allenols with Silylzinc Reagents: Access to 2-Silyl-1,3-butadienes

   Xu, Guang-Li; Duan, Yu-Tong; Wang, Zhong-Xia

   Organic Letters (2022), 24 (43), 7934-7938CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)

   Reaction of 2,3-allenols with PhMe2SiZnCl or Ph2MeSiZnCl under catalysis of IPrCuCl or SIPrCuCl was carried out, affording 2-silyl-1,3-butadienes. Secondary and tertiary 2,3-allenols could be used as coupling partners. Reaction of secondary 2,3-allenols gave (E)-2-silyl-1,3-butadienes as the only products.

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   (b) Jia, J.; Yuan, F.; Zhang, Z.; Song, X.; Hu, F.; Xia, Y. Copper-Catalyzed Ring-Opening Defluoroborylation of gem-Difluorinated Cyclobutenes: A General Route to Bifunctional 1,3-Dienes and Their Applications. Org. Lett. 2022, 24, 1985– 1990,  DOI: 10.1021/acs.orglett.2c00403

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   8b

   Copper-Catalyzed Ring-Opening Defluoroborylation of gem-Difluorinated Cyclobutenes: A General Route to Bifunctional 1,3-Dienes and Their Applications

   Jia, Jie; Yuan, Fushan; Zhang, Zihao; Song, Xuejiao; Hu, Fangdong; Xia, Ying

   Organic Letters (2022), 24 (10), 1985-1990CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)

   The exploration of the reactivity of gem-difluorinated small-size rings has continuously drawn attention in recent years but is limited to three-membered carbocycles. Herein, the authors report a Cu-catalyzed reaction of gem-fluorinated cyclobutenes with bis(pinacolato)diboron (B2pin2). A sequence of defluoroborylation and ring opening process produces B,F-bifunctional 1,3-dienes in a stereoselective manner. The transformation together with the efficient downstream coupling of the boronate and the fluoride moiety collectively constitutes a modular route to highly functionalized and stereocontrolled 1,3-dienes.

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   (c) Shan, Q.-C.; Hu, L.-M.; Qin, W.; Hu, X.-H. Copper-Catalyzed Cross-Nucleophile Coupling of β-Allenyl Silanes with Tertiary C–H Bonds: A Radical Approach to Branched 1,3-Dienes. Org. Lett. 2021, 23, 6041– 6045,  DOI: 10.1021/acs.orglett.1c02112

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   8c

   Copper-Catalyzed Cross-Nucleophile Coupling of β-Allenyl Silanes with Tertiary C-H Bonds: A Radical Approach to Branched 1,3-Dienes

   Shan, Qi-Chao; Hu, Lu-Min; Qin, Wei; Hu, Xu-Hong

   Organic Letters (2021), 23 (15), 6041-6045CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)

   A distinctive approach to branched 1,3-dienes through oxidative coupling of two nucleophilic substrates, β-allenyl silanes, and hydrocarbons appending latent functionality by copper catalysis were described. Notably, C(sp3)-H dienylation proceeded in a regiospecific manner, even in the presence of competitive C-H bonds that were capable of occurring hydrogen atom transfer process, such as those located at benzylic and other tertiary sites, or adjacent to an oxygen atom. Control expts. supported the intermediacy of functionalized alkyl radicals.

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   (d) Guo, K.; Kleij, A. W. Copper-Mediated Dichotomic Borylation of Alkyne Carbonates: Stereoselective Access to (E)-1,2-Diborylated 1,3-Dienes versus Traceless Monoborylation Affording α-Hydroxyallenes. Angew. Chem., Int. Ed. 2021, 60, 4901– 4906,  DOI: 10.1002/anie.202014310

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   8d

   Copper-Mediated Dichotomic Borylation of Alkyne Carbonates: Stereoselective Access to (E)-1,2-Diborylated 1,3-Dienes versus Traceless Monoborylation Affording α-Hydroxyallenes

   Guo, Kun; Kleij, Arjan W.

   Angewandte Chemie, International Edition (2021), 60 (9), 4901-4906CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

   A mild copper-mediated protocol has been developed for borylation of alkynyl cyclic carbonates I, affording diborylated 1,3-dienes II [R1 = PhCH2CH2, alkyl; R2, R3 = H, alkyl, R2-R3 = (CH2)4, (CH2)5] in reaction with B2pin2 and α-hydroxyallenes R1CH:C:CR2CH(OH)R3 in reaction with B2neop2. Depending on the nature of the borylating reaction partner, either stereoselective diborylation of the propargylic surrogate takes place, providing convenient access to (E)-1,2-borylated 1,3-dienes, or traceless monoborylation occurs, which leads to α-hydroxyallenes as the principal product. The dichotomy in this borylation protocol has been scrutinized by several control expts., illustrating that a relatively small change in the diboron(4) reagent allows for competitive alc.-assisted protodemetalation to forge an α-hydroxyallene product under ambient conditions.

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   (e) Chaves-Pouso, A.; Rivera-Chao, E.; Fañanás-Mastral, M. Copper-catalyzed protoboration of borylated dendralenes: a regio- and stereoselective access to functionalized 1,3-dienes. Chem. Commun. 2020, 56, 12230– 12233,  DOI: 10.1039/D0CC04018E

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   8e

   Copper-catalyzed protoboration of borylated dendralenes: a regio- and stereoselective access to functionalized 1,3-dienes

   Chaves-Pouso, Andrea; Rivera-Chao, Eva; Fananas-Mastral, Martin

   Chemical Communications (Cambridge, United Kingdom) (2020), 56 (81), 12230-12233CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)

   A Cu-catalyzed protoboration of borylated dendralenes is reported. The method employs an NHC-Cu catalyst and provides access to 1,4-addn. products with excellent levels of chemo-, regio- and stereoselectivity. The resulting diene bis(boronates) are oxidized to the corresponding diene diols which are synthetically versatile building blocks.

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   (f) Chen, F.; Xia, Y.; Lin, R.; Gao, Y.; Xu, P.; Zhao, Y. Copper-Catalyzed Direct Twofold C–P Cross-Coupling of Unprotected Propargylic 1,4-Diols: Access to 2,3-Bis(diarylphosphynyl)-1,3-butadienes. Org. Lett. 2019, 21, 579– 583,  DOI: 10.1021/acs.orglett.8b03985

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   8f

   Copper-Catalyzed Direct Twofold C-P Cross-Coupling of Unprotected Propargylic 1,4-Diols: Access to 2,3-Bis(diarylphosphinyl)-1,3-butadienes

   Chen, Fushan; Xia, Ying; Lin, Rongcan; Gao, Yuxing; Xu, Pengxiang; Zhao, Yufen

   Organic Letters (2019), 21 (2), 579-583CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)

   The 1st facile and efficient Cu-catalyzed direct coupling of unprotected propargylic diols with H-phosphine oxides was developed, providing a practical approach to access structurally diverse 2,3-bis(diarylphosphinyl)-1,3-butadienes along with the formation of two new P-Csp2 and two new C:C bonds under ligand- and base-free conditions.

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   (g) Semba, K.; Fujihara, T.; Terao, J.; Tsuji, Y. Copper-Catalyzed Borylation of α-Alkoxy Allenes with Bis(pinacolato)diboron: Efficient Synthesis of 2-Boryl 1,3-Butadienes. Angew. Chem., Int. Ed. 2013, 52, 12400– 12403,  DOI: 10.1002/anie.201306843

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   8g

   Copper-catalyzed borylation of α-alkoxy allenes with bis(pinacolato)diboron: efficient synthesis of 2-boryl 1,3-butadienes

   Semba, Kazuhiko; Fujihara, Tetsuaki; Terao, Jun; Tsuji, Yasushi

   Angewandte Chemie, International Edition (2013), 52 (47), 12400-12403CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

   Borylation of allenes R1R2C:C:CR5CR3R4OCH2Ph (1) with B2(pin)2, catalyzed by 0.01-0.05 mol% of copper(I) N-heterocyclic carbene (L) complexes [LCuCl] comprises cleavage of the benzyloxy group and afforded 1,3-butadien-2-ylboronates R1R2C:C(Bpin)CR5:CR3R4 [2, R1, R2 = H, Me, R1-R2 = (CH2)5; R3, R4 = H, Me, iPr, R3-R4 = CH2CH2NBocCH2CH2; R5 = H, Bu, Ph] with 59-99% yields. Unsym. α,α-disubstituted allenes (1l, R1 = R2 = H, R3 = Me, R4 = Ph, R5 = H; 1k, R1 = R2 = H, R3 = Me, R4 = iPr, R5 = H) gave only the corresponding (E)-isomers 2l and 2k in 63 and 96% yields, resp. (E/Z = 96:4, 90:10). Reaction mechanism, comprising formation of copper boryl complexes [LCuBpin] with subsequent addn. across C2-C3 double bond of the allylic system with subsequent β-elimination of the benzyloxycopper complex [LCuOCH2Ph] is suggested.

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9. 9

   (a) Zhou, Z.; Chen, J.; Chen, H.; Kong, W. Stereoselective Synthesis of Pentasubstituted 1,3-Dienes via Ni-catalyzed Reductive Coupling of Unsymmetrical Internal Alkynes. Chem. Sci. 2020, 11, 10204– 10211,  DOI: 10.1039/D0SC04173D

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   9a

   Stereoselective synthesis of pentasubstituted 1,3-dienes via Ni-catalyzed reductive coupling of unsymmetrical internal alkynes

   Zhou, Zhijun; Chen, Jiachang; Chen, Herong; Kong, Wangqing

   Chemical Science (2020), 11 (37), 10204-10211CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)

   The nickel-catalyzed reductive coupling of two unsym. internal alkynes overcomed the above-mentioned limitations by using a hemilabile directing group strategy to control the regioselectivity was reported. A series of synthetically challenging penta-substituted 1,3-dienes were obtained in good yields with high regio- and enantioselectivity (mostly > 20/1 rr, >90% ee).

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   (b) Chen, Y.; Dang, L.; Ho, C.-Y. NHC-Ni Catalyzed Enantioselective Synthesis of 1,4-Dienes by Cross-Hydroalkenylation of Cyclic 1,3-Dienes and Heterosubstituted Terminal Olefins. Nat. Commun. 2020, 11, 2269,  DOI: 10.1038/s41467-020-16139-2

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   9b

   NHC-Ni catalyzed enantioselective synthesis of 1,4-dienes by cross-hydroalkenylation of cyclic 1,3-dienes and heterosubstituted terminal olefins

   Chen, Yang; Dang, Liang; Ho, Chun-Yu

   Nature Communications (2020), 11 (1), 2269CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)

   An enantioselective cross-hydroalkenylation of cyclic 1,3-dienes and hetero-substituted terminal olefins by using a chiral [NHC-Ni(allyl)]BArF catalyst was reported. Using a structurally flexible chiral C2 NHC-Ni design was key to access a broad scope of chiral 1,4-dienes with high enantioselectivity. This study also offered insights on how to regulated chiral C2 NHC-Ni(II) 1,3-allylic shift on cyclic diene and to build sterically more hindered endocyclic chiral allylic structures on demand.

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   (c) Francos, J.; Cadierno, V. Nickel-Catalyzed Homocoupling of (Z)-β-Iodoenol Esters: Stereoselective Access to (Z, Z)-Buta-1, 3-diene-1, 4-diyl diesters. Synthesis 2019, 51, 3117– 3126,  DOI: 10.1055/s-0037-1610709

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   9c

   Nickel-Catalyzed Homocoupling of (Z)-β-Iodoenol Esters: Stereoselective Access to (Z,Z)-Buta-1,3-diene-1,4-diyl Diesters

   Francos, Javier; Cadierno, Victorio

   Synthesis (2019), 51 (16), 3117-3126CODEN: SYNTBF; ISSN:1437-210X. (Georg Thieme Verlag)

   A straightforward and broad-scope procedure to obtain sym. substituted buta-1,3-diene-1,4-diyl diesters, based on the homocoupling of the corresponding (Z)-β-iodoenol esters, was presented. It involved the use of a catalytic system composed of [NiCl2(PPh3)2] (10 mol%), NaI (10 mol%), and excess Zn dust. The reactions proceed in THF at room temp. with exquisite preservation of the stereochem. of the C=C bond of the starting iodoolefins, thus leading to the final dienes as the corresponding Z,Z-stereoisomers exclusively.

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   (d) Watabe, Y.; Kanazawa, K.; Fujita, T.; Ichikawa, J. Nickel-Catalyzed Hydroalkenylation of Alkynes through C–F Bond Activation: Synthesis of 2-Fluoro-1, 3-dienes. Synthesis 2017, 49, 3569– 3575,  DOI: 10.1055/s-0036-1588842

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   9d

   Nickel-Catalyzed Hydroalkenylation of Alkynes through C-F Bond Activation: Synthesis of 2-Fluoro-1,3-dienes

   Watabe, Yota; Kanazawa, Kohei; Fujita, Takeshi; Ichikawa, Junji

   Synthesis (2017), 49 (16), 3569-3575CODEN: SYNTBF; ISSN:1437-210X. (Georg Thieme Verlag)

   2-Fluoro-1,3-dienes were synthesized through nickel-catalyzed coupling reactions between β,β-difluorostyrenes and alkynes in the presence of ZrF4 as co-catalyst and a hydride source derived from triethylborane and lithium isopropoxide. Mechanistic studies revealed that the carbon-fluorine bond was cleaved by β-fluorine elimination from intermediary nickelacyclopentenes generated through oxidative cyclization of the two substrates.

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   (e) Kawashima, T.; Ohashi, M.; Ogoshi, S. Nickel-Catalyzed Formation of 1,3-Dienes via a Highly Selective Cross-Tetramerization of Tetrafluoroethylene, Styrenes, Alkynes, and Ethylene. J. Am. Chem. Soc. 2017, 139, 17795– 17798,  DOI: 10.1021/jacs.7b12007

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   9e

   Nickel-Catalyzed Formation of 1,3-Dienes via a Highly Selective Cross-Tetramerization of Tetrafluoroethylene, Styrenes, Alkynes, and Ethylene

   Kawashima, Takuya; Ohashi, Masato; Ogoshi, Sensuke

   Journal of the American Chemical Society (2017), 139 (49), 17795-17798CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   In the presence of a catalytic amt. of Ni(cod)2 (cod = 1,5-cyclooctadiene) and PCy3 (Cy = cyclohexyl), the cross-tetramerization of tetrafluoroethylene (TFE), alkynes, and ethylene occurred in a highly selective manner to afford a variety of 1,3-dienes with a 3,3,4,4-tetrafluorobutyl chain. In addn., a Ni(0)-catalyzed cross-tetramerization of TFE, alkynes, ethylene, and styrenes was developed. These catalytic reactions might proceed via partially fluorinated five- and seven-membered nickelacycle key intermediates.

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   (f) Ogata, K.; Murayama, H.; Sugasawa, J.; Suzuki, N.; Fukuzawa, S.-i. Nickel-Catalyzed Highly Regio- and Stereoselective Cross-Trimerization between Triisopropylsilylacetylene and Internal Alkynes Leading to 1,3-Diene-5-ynes. J. Am. Chem. Soc. 2009, 131, 3176– 3177,  DOI: 10.1021/ja900146u

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   9f

   Nickel-catalyzed highly regio- and stereoselective cross-trimerization between triisopropylsilylacetylene and internal alkynes leading to 1,3-diene-5-ynes

   Ogata, Kenichi; Murayama, Hiroyuki; Sugasawa, Jun; Suzuki, Noriyuki; Fukuzawa, Shin-Ichi

   Journal of the American Chemical Society (2009), 131 (9), 3176-3177CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

   The first highly selective 1:2 cross-trimerization between triisopropylsilylacetylene and 2 equiv of internal alkynes, leading to 1,3-diene-5-yne compds., was achieved using the Ni(cod)2/PnPr3 catalyst. Various sym. and asym. internal alkynes could be used for the cross-trimerization reaction with high regio- and stereoselectivity.

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   (g) Ananikov, V. P.; Orlov, N. V.; Kabeshov, M. A.; Beletskaya, I. P.; Starikova, Z. A. Stereodefined Synthesis of a New Type of 1,3-Dienes by Ligand-Controlled Carbon–Carbon and Carbon–Heteroatom Bond Formation in Nickel-Catalyzed Reaction of Diaryldichalcogenides with Alkynes. Organometallics 2008, 27, 4056– 4061,  DOI: 10.1021/om800282h

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   9g

   Stereodefined Synthesis of a New Type of 1,3-Dienes by Ligand-Controlled Carbon-Carbon and Carbon-Heteroatom Bond Formation in Nickel-Catalyzed Reaction of Diaryldichalcogenides with Alkynes

   Ananikov, Valentine P.; Orlov, Nikolay V.; Kabeshov, Mikhail A.; Beletskaya, Irina P.; Starikova, Zoya A.

   Organometallics (2008), 27 (16), 4056-4061CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)

   It was found that ligand control over the carbon-carbon and carbon-heteroatom bond formation on the nickel center provides an easy and convenient route to sym. (minor) and unsym. (major) isomers of sulfur- and selenium-substituted 1,3-dienes. The unsym. product is a new type of 1,4-substituted conjugated diene, which was readily synthesized from alkynes and diaryldichalcogenides. The unique feature of this developed one-pot transformation is total stereodefined synthesis of the diene skeleton, controlling not only the configuration of the double bond but also the s-gauche conformation of the central C-C bond. The mechanistic study revealed the key feature of alkyne insertion into the Ni-E and Ni-C bonds (E = S, Se), which governs the direction of the chem. transformation. Thus, Ni(acac)2/PPhCy2 catalyzed reaction of 1-hexyne with Ph2S2 in MeCN gave 70% [(Z,Z-2-butyl-4-(phenylsulfanyl)-1,3-octadienyl)sulfanyl]benzene.

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   (h) Ikeda, Y.; Ukai, J.; Ikeda, N.; Yamamoto, H. Stereoselective Synthesis of 1,4-Disubstituted 1,3-Diene from Aldehyde Using Organotitanium Reagent. Tetrahedron 1987, 43, 731– 741,  DOI: 10.1016/S0040-4020(01)90007-9

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   9h

   Stereoselective synthesis of 1,4-disubstituted 1,3-diene from aldehyde using an organotitanium reagent

   Ikeda, Yoshihiko; Ukai, Junzo; Ikeda, Nobuo; Yamamoto, Hisashi

   Tetrahedron (1987), 43 (4), 731-41CODEN: TETRAB; ISSN:0040-4020.

   The organotitanium reagent generated from Me3CSCH:CHCH2SiMe3 and Ti(OR)4 condenses with RCHO [R = cyclohexyl, (E)-MeCH:CH, hexyl] to give (E)-erythro-β-hydroxysilanes which eliminate Me3SiOH to give (E,Z)-Me3CSCH:CHCH:CHR (I; same R) regio- and stereoselectively. (E,Z)-1,4-Dialkyl-1,3-dienes are obtained from I by cross coupling with a Grignard reagent in the presence of a Ni catalyst. Spilanthol, a naturally occurring insecticide from Spilanthese olerancae, is prepd. in 5 steps by this method.

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10. 10

    (a) Fürstner, A. Iron Catalyzed C–C-Bond Formation: From Canonical Cross Coupling to a Quest for New Reactivity. Bull. Chem. Soc. Jpn. 2021, 94, 666– 677,  DOI: 10.1246/bcsj.20200319

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    10a

    Iron Catalyzed C-C-Bond Formation: From Canonical Cross Coupling to a Quest for New Reactivity

    Fuerstner, Alois

    Bulletin of the Chemical Society of Japan (2021), 94 (2), 666-677CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)

    A review. This account summarizes our work in the area of organoiron chem. during the last two decades, with special emphasis on iron catalyzed C-C-bond formation. Specifically, it is shown that iron catalysts can emulate reactivity more befitting noble metals in that they allow various cross coupling, cycloaddn. and cycloisomerization reactions to be carried out with surprising ease. At the same time, this base metal opens opportunities for the discovery of genuinely new transformations.

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    (b) Sandl, S.; Jacobi von Wangelin, A. The Role of Organoferrates in Iron-Catalyzed Cross-Couplings. Angew. Chem., Int. Ed. 2020, 59, 5434– 5437,  DOI: 10.1002/anie.201914844

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    10b

    The Role of Organoferrates in Iron-Catalyzed Cross-Couplings

    Sandl, Sebastian; Jacobi von Wangelin, Axel

    Angewandte Chemie, International Edition (2020), 59 (14), 5434-5437CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    There is no expanded citation for this reference.

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    (c) Neidig, M. L.; Carpenter, S. H.; Curran, D. J.; DeMuth, J. C.; Fleischauer, V. E.; Iannuzzi, T. E.; Neate, P. G.; Sears, J. D.; Wolford, N. J. Development and Evolution of Mechanistic Understanding in Iron-Catalyzed Cross-Coupling. Acc. Chem. Res. 2019, 52, 140– 150,  DOI: 10.1021/acs.accounts.8b00519

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    10c

    Development and Evolution of Mechanistic Understanding in Iron-Catalyzed Cross-Coupling

    Neidig, Michael L.; Carpenter, Stephanie H.; Curran, Daniel J.; DeMuth, Joshua C.; Fleischauer, Valerie E.; Iannuzzi, Theresa E.; Neate, Peter G. N.; Sears, Jeffrey D.; Wolford, Nikki J.

    Accounts of Chemical Research (2019), 52 (1), 140-150CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)

    Since the pioneering work of Kochi in the 1970s, iron has attracted great interest for cross-coupling catalysis due to its low cost and toxicity as well as its potential for novel reactivity compared to analogous reactions with precious metals like palladium. Today there are numerous iron-based cross-coupling methodologies available, including challenging alkyl-alkyl and enantioselective methods. Furthermore, cross-couplings with simple ferric salts and additives like NMP and TMEDA (N-methylpyrrolidone and tetramethylethylenediamine) continue to attract interest in pharmaceutical applications. Despite the tremendous advances in iron cross-coupling methodologies, in situ formed and reactive iron species and the underlying mechanisms of catalysis remain poorly understood in many cases, inhibiting mechanism-driven methodol. development in this field.This lack of mechanism-driven development has been due, in part, to the challenges of applying traditional characterization methods such as NMR (NMR) spectroscopy to iron chem. due to the multitude of paramagnetic species that can form in situ. The application of a broad array of inorg. spectroscopic methods (e.g., ESR, 57Fe M.ovrddot.ossbauer, and magnetic CD) removes this barrier and has revolutionized our ability to evaluate iron speciation. In conjunction with inorg. syntheses of unstable organoiron intermediates and combined inorg. spectroscopy/gas chromatog. studies to evaluate in situ iron reactivity, this approach has dramatically evolved our understanding of in situ iron speciation, reactivity, and mechanisms in iron-catalyzed cross-coupling over the past 5 years.This Account focuses on the key advances made in obtaining mechanistic insight in iron-catalyzed carbon-carbon cross-couplings using simple ferric salts, iron-bisphosphines, and iron-N-heterocyclic carbenes (NHCs). Our studies of ferric salt catalysis have resulted in the isolation of an unprecedented iron-Me cluster, allowing us to identify a novel reaction pathway and solve a decades-old mystery in iron chem. NMP has also been identified as a key to accessing more stable intermediates in reactions contg. nucleophiles with and without β-hydrogens. In iron-bisphosphine chem., we have identified several series of transmetalated iron(II)-bisphosphine complexes contg. mesityl, Ph, and alkynyl nucleophile-derived ligands, where mesityl systems were found to be unreliable analogs to phenyls. Finally, in iron-NHC cross-coupling, unique chelation effects were obsd. in cases where nucleophile-derived ligands contained coordinating functional groups. As with the bisphosphine case, high-spin iron(II) complexes were shown to be reactive and selective in cross-coupling. Overall, these studies have demonstrated key aspects of iron cross-coupling and the utility of detailed speciation and mechanistic studies for the rational improvement and development of iron cross-coupling methods.

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11. 11

    (a) Manna, S.; Kong, W.-J.; Bäckvall, J.-E. Iron (II)-Catalyzed Aerobic Biomimetic Oxidation of N-Heterocycles. Chem. Eur. J. 2021, 27, 13725– 13729,  DOI: 10.1002/chem.202102483

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    11a

    Iron(II)-Catalyzed Aerobic Biomimetic Oxidation of N-Heterocycles

    Manna, Srimanta; Kong, Wei-Jun; Backvall, Jan-E.

    Chemistry - A European Journal (2021), 27 (55), 13725-13729CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Herein, an iron(II)-catalyzed biomimetic oxidn. of N-heterocycles under aerobic conditions was described. The dehydrogenation process, involving several electron-transfer steps was inspired by oxidns. occurring in the respiratory chain. An environmentally friendly and inexpensive iron catalyst together with a hydroquinone/cobalt Schiff base hybrid catalyst as electron-transfer mediator were used for the substrate-selective dehydrogenation reaction of various N-heterocycles. The method shows a broad substrate scope and delivers important heterocycles in good-to-excellent yields.

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    (b) Gudmundsson, A.; Manna, S.; Bäckvall, J. E. Iron (II)-Catalyzed Aerobic Biomimetic Oxidation of Amines using a Hybrid Hydroquinone/Cobalt Catalyst as Electron Transfer Mediator. Angew. Chem. 2021, 133, 11925– 11929,  DOI: 10.1002/ange.202102681

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    (c) Gudmundsson, A.; Schlipköter, K. E.; Bäckvall, J.-E. Iron(II)-Catalyzed Biomimetic Aerobic Oxidation of Alcohols. Angew. Chem., Int. Ed. 2020, 59, 5403– 5406,  DOI: 10.1002/anie.202000054

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    11c

    Iron(II)-Catalyzed Biomimetic Aerobic Oxidation of Alcohols

    Gudmundsson Arnar; Schlipkoter Kim Elisabeth; Backvall Jan-E; Schlipkoter Kim Elisabeth

    Angewandte Chemie (International ed. in English) (2020), 59 (13), 5403-5406 ISSN:.

    We report the first Fe(II) -catalyzed biomimetic aerobic oxidation of alcohols. The principle of this oxidation, which involves several electron-transfer steps, is reminiscent of biological oxidation in the respiratory chain. The electron transfer from the alcohol to molecular oxygen occurs with the aid of three coupled catalytic redox systems, leading to a low-energy pathway. An iron transfer-hydrogenation complex was utilized as a substrate-selective dehydrogenation catalyst, along with an electron-rich quinone and an oxygen-activating Co(salen)-type complex as electron-transfer mediators. Various primary and secondary alcohols were oxidized in air to the corresponding aldehydes or ketones with this method in good to excellent yields.

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    (d) Jiang, X.; Zhang, J.; Ma, S. Iron Catalysis for Room-Temperature Aerobic Oxidation of Alcohols to Carboxylic Acids. J. Am. Chem. Soc. 2016, 138, 8344– 8347,  DOI: 10.1021/jacs.6b03948

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    11d

    Iron Catalysis for Room-Temperature Aerobic Oxidation of Alcohols to Carboxylic Acids

    Jiang, Xingguo; Zhang, Jiasheng; Ma, Shengming

    Journal of the American Chemical Society (2016), 138 (27), 8344-8347CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Oxidn. from alcs. to carboxylic acids, a class of essential chems. in daily life, academic labs., and industry, is a fundamental reaction, usually using at least a stoichiometric amt. of an expensive and toxic oxidant. Here, an efficient and practical sustainable oxidn. technol. of alcs. to carboxylic acids using pure O2 or even O2 in air as the oxidant has been developed: utilizing a catalytic amt. each of Fe(NO3)3·9H2O/TEMPO/MCl, a series of carboxylic acids were obtained from alcs. (also aldehydes) in high yields at room temp. A 55 g-scale reaction was demonstrated using air. As a synthetic application, the first total synthesis of a naturally occurring allene, i.e., phlomic acid, was accomplished.

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12. 12

    (a) Shang, R.; Ilies, L.; Nakamura, E. Iron-Catalyzed C–H Bond Activation. Chem. Rev. 2017, 117, 9086– 9139,  DOI: 10.1021/acs.chemrev.6b00772

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    12a

    Iron-Catalyzed C-H Bond Activation

    Shang, Rui; Ilies, Laurean; Nakamura, Eiichi

    Chemical Reviews (Washington, DC, United States) (2017), 117 (13), 9086-9139CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    A review. This review summarizes the development of stoichiometric C-H activation that has a long history, and catalytic C-H functionalization that emerged about ten years ago. Reactions that take place via reactive organoiron intermediates, and excluded those using iron as a Lewis acid or radical initiator was focused. The contents of this review are categorized by the type of C-H bond cleaved and the type of bond formed thereafter, and covers the reactions of simple substrates and substrates possessing a directing group that anchors the catalyst to the substrate, providing an overview of iron-mediated and -catalyzed C-H activation reported in the literature by Oct. of 2016.

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    (b) Cera, G.; Ackermann, L. Iron-Catalyzed C–H Functionalization Processes. In Ni- and Fe-Based Cross-Coupling Reactions; Springer, 2017; pp 191– 224.

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13. 13

    (a) Isomura, M.; Petrone, D. A.; Carreira, E. M. Construction of Vicinal Quaternary Centers via Iridium-Catalyzed Asymmetric Allenylic Alkylation of Racemic Tertiary Alcohols. J. Am. Chem. Soc. 2021, 143, 3323– 3329,  DOI: 10.1021/jacs.1c00609

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    13a

    Construction of Vicinal Quaternary Centers via Iridium-Catalyzed Asymmetric Allenylic Alkylation of Racemic Tertiary Alcohols

    Isomura, Mayuko; Petrone, David A.; Carreira, Erick M.

    Journal of the American Chemical Society (2021), 143 (9), 3323-3329CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Enantioselective bond formation between sterically hindered fragments to furnish acyclic products with vicinal quaternary centers is a formidable challenge. We report a soln. that involves cocatalysis between a chiral Ir-(phosphoramidite, olefin) complex and La(OTf)3. This robust catalytic system effects highly enantioconvergent and regioselective alkylation of racemic tertiary α-allenyl alcs. with tetrasubstituted silyl ketene acetals. The transformation displays broad functional group tolerance for both reaction components and allows efficient generation of β-allenyl ester products in good yield and with excellent enantioselectivity. Furthermore, both the allene and ester functionalities were leveraged to upgrade the structural complexity of the products via a series of stereoselective metal-catalyzed functionalization reactions.

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    (b) Petrone, D. A.; Isomura, M.; Franzoni, I.; Rössler, S. L.; Carreira, E. M. Allenylic Carbonates in Enantioselective Iridium-Catalyzed Alkylations. J. Am. Chem. Soc. 2018, 140, 4697– 4704,  DOI: 10.1021/jacs.8b01416

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    13b

    Allenylic Carbonates in Enantioselective Iridium-Catalyzed Alkylations

    Petrone, David A.; Isomura, Mayuko; Franzoni, Ivan; Rossler, Simon L.; Carreira, Erick M.

    Journal of the American Chemical Society (2018), 140 (13), 4697-4704CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    An enantioconvergent C(sp3)-C(sp3) coupling between racemic allenylic electrophiles and alkylzinc reagents has been developed. An Ir/(phosphoramidite,olefin) catalyst provides access to highly enantioenriched allenylic substitution products (93-99% ee) with complete regiocontrol (>50:1 rr in all cases) over the undesired 1,3-dienes isomers which are obtained predominantly in the case of other metal catalysts. The synthetic utility of the products obtained was highlighted in a variety of stereoselective transition metal-catalyzed difunctionalization reactions. Furthermore, a combination of computational and exptl. studies supports a putative reaction mechanism wherein enantiodetermining C-C coupling occurs via nucleophilic attack on a highly planarized aryl butadienyl π-system that is coordinated to the Ir center in an η2-fashion.

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    (c) Li, Q.; Fu, C.; Ma, S. Catalytic Asymmetric Allenylation of Malonates with the Generation of Central Chirality. Angew. Chem., Int. Ed. 2012, 51, 11783– 11786,  DOI: 10.1002/anie.201204346

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    13c

    Catalytic asymmetric allenylation of malonates with the generation of central chirality

    Li, Qiankun; Fu, Chunling; Ma, Shengming

    Angewandte Chemie, International Edition (2012), 51 (47), 11783-11786CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A highly enantioselective allenylation of di-Et malonate with racemic 2,3-allenyl acetates is developed. The merits of this method includes broad functional group tolerance, mild reaction conditions, and the availability of starting materials.

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    (d) Nemoto, T.; Kanematsu, M.; Tamura, S.; Hamada, Y. Palladium-Catalyzed Asymmetric Allylic Alkylation of 2, 3-Allenyl Acetates Using a Chiral Diaminophosphine Oxide. Adv. Synth. Catal. 2009, 351, 1773– 1778,  DOI: 10.1002/adsc.200900151

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    13d

    Palladium-Catalyzed Asymmetric Allylic Alkylation of 2,3-Allenyl Acetates Using a Chiral Diaminophosphine Oxide

    Nemoto, Tetsuhiro; Kanematsu, Mutsumi; Tamura, Shinji; Hamada, Yasumasa

    Advanced Synthesis & Catalysis (2009), 351 (11+12), 1773-1778CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)

    An enantioselective synthesis of allenes through palladium-catalyzed asym. allylic alkylation using a chiral diaminophosphine oxide is described. The asym. allylic alkylations proceeded in the presence of a catalytic amt. of lithium acetate at 4 °C, affording the chiral allenes in excellent yield with up to 99% ee.

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    (e) Trost, B. M.; Fandrick, D. R.; Dinh, D. C. Dynamic Kinetic Asymmetric Allylic Alkylations of Allenes. J. Am. Chem. Soc. 2005, 127, 14186– 14187,  DOI: 10.1021/ja0543705

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    13e

    Dynamic kinetic asymmetric allylic alkylation of allenes

    Trost, Barry M.; Fandrick, Daniel R.; Dinh, Diana C.

    Journal of the American Chemical Society (2005), 127 (41), 14186-14187CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The dynamic kinetic asym. allylic alkylation of racemic allene acetates has been developed with the DACH-Ph Trost ligand 2 to give general access to allenes with high enantiomeric excess (84-95%) for both malonate and amine nucleophiles. Further, a most unusual dependence of enantioselectivity on base has been uncovered. The magnitude of the enantioselectivity is heavily dependent on the base for the malonate nucleophiles, but the sense and magnitude of the asym. induction is dependent on the base for the amine nucleophiles. A Rh(I)-catalyzed intramol. [4+2] cycloaddn. of the DYKAT products was accomplished to afford formal Diels-Alder adducts, wherein the axial chirality is faithfully transferred into multiple stereogenic centers as well as olefin geometry.

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    (f) Kezuka, S.; Kanemoto, K.; Takeuchi, R. Iridium Complex-Catalyzed Method for the Construction of a Quaternary Carbon Center α to Allene. Tetrahedron Lett. 2004, 45, 6403– 6406,  DOI: 10.1016/j.tetlet.2004.07.002

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    13f

    Iridium complex-catalyzed method for the construction of a quaternary carbon center α to allene

    Kezuka, Satoko; Kanemoto, Kazuyuki; Takeuchi, Ryo

    Tetrahedron Letters (2004), 45 (34), 6403-6406CODEN: TELEAY; ISSN:0040-4039. (Elsevier)

    [Ir(cod)Cl]2/dppe-catalyzed allylic alkylation of 1,1-disubstituted-2,3-butadienyl acetates gave alkylated products, e.g., I, bearing a quaternary carbon center α to allene in high yield.

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    (g) Imada, Y.; Ueno, K.; Kutsuwa, K.; Murahashi, S.-I. Palladium-Catalyzed Asymmetric Alkylation of 2,3-Alkadienyl Phosphates. Synthesis of Optically Active 2-(2,3-Alkadienyl)malonates. Chem. Lett. 2002, 31, 140– 141,  DOI: 10.1246/cl.2002.140

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14. 14

    (a) Alonso, J. M.; Almendros, P. Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality. Chem. Rev. 2021, 121, 4193– 4252,  DOI: 10.1021/acs.chemrev.0c00986

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    14a

    Deciphering the Chamaleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

    Alonso, Jose M.; Almendros, Pedro

    Chemical Reviews (Washington, DC, United States) (2021), 121 (7), 4193-4252CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    A review. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This review summarizes the most significant contributions to the chem. of allenols appeared during the past decade, with emphasis on their synthesis, reactivity and occurrence in natural products.

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    (b) Shukla, R. K.; Nair, A. M.; Khan, S.; Volla, C. M. Cobalt-Catalyzed C8-Dienylation of Quinoline-N-Oxides. Angew. Chem., Int. Ed. 2020, 132, 17190– 17196,  DOI: 10.1002/ange.202003216

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    (c) Lippincott, D. J.; Linstadt, R. T.; Maser, M. R.; Gallou, F.; Lipshutz, B. H. Synthesis of Functionalized 1, 3-Butadienes via Pd-Catalyzed Cross-Couplings of Substituted Allenic Esters in Water at Room Temperature. Org. Lett. 2018, 20, 4719– 4722,  DOI: 10.1021/acs.orglett.8b01377

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    14c

    Synthesis of Functionalized 1,3-Butadienes via Pd-Catalyzed Cross-Couplings of Substituted Allenic Esters in Water at Room Temperature

    Lippincott, Daniel J.; Linstadt, Roscoe T. H.; Maser, Michael R.; Gallou, Fabrice; Lipshutz, Bruce H.

    Organic Letters (2018), 20 (16), 4719-4722CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)

    An environmentally responsible, mild method for the synthesis of functionalized 1,3-butadienes is presented. It utilizes allenic esters of varying substitution patterns, as well as a wide range of boron-based nucleophiles under palladium catalysis, generating sp-sp2, sp2-sp2, and sp2-sp3 bonds. Functional group tolerance measured via robustness screening, along with room temp. and aq. reaction conditions highlight the methodol.'s breadth and potential utility in synthesis.

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    (d) Sim, S. H.; Park, H.-J.; Lee, S. I.; Chung, Y. K. Palladium (0)-Catalyzed Decarboxylation of Buta-2, 3-dienyl 2’-Alkynoates: Approach to the Synthesis of 2-Alkynyl Buta-1, 3-dienes. Org. Lett. 2008, 10, 433– 436,  DOI: 10.1021/ol702577g

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    14d

    Palladium(0)-Catalyzed Decarboxylation of Buta-2,3-dienyl 2'-Alkynoates: Approach to the Synthesis of 2-Alkynyl Buta-1,3-dienes

    Sim, So Hee; Park, Hee-Jun; Lee, Sang Ick; Chung, Young Keun

    Organic Letters (2008), 10 (3), 433-436CODEN: ORLEF7; ISSN:1523-7060. (American Chemical Society)

    The Pd(PPh3)4-catalyzed decarboxylation of buta-2,3-dienyl 2'-alkynoates allows the rapid construction of 2-alkynyl buta-1,3-dienes, e.g., I. The carbon-carbon bond-forming reaction occurs at the central position of an allene moiety.

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    (e) Schneekloth, J. S., Jr; Pucheault, M.; Crews, C. M. Construction of Highly Substituted Stereodefined Dienes by Cross-Coupling of α-Allenic Acetates. Eur. J. Org. Chem. 2007, 2007, 40– 43,  DOI: 10.1002/ejoc.200600721

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    (f) Moriya, T.; Furuuchi, T.; Miyaura, N.; Suzuki, A. A New Facile Synthesis of 2-Substituted 1, 3-Butadiene Derivatives via Palladium-Catalyzed Cross-Coupling Reaction of 2, 3-Alkadienyl Carbonates with Organoboron Compounds. Tetrahedron 1994, 50, 7961– 7968,  DOI: 10.1016/S0040-4020(01)85281-9

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    14f

    A new facile synthesis of 2-substituted 1,3-butadiene derivatives via palladium-catalyzed cross-coupling reaction of 2,3-alkadienyl carbonates with organoboron compounds

    Moriya, Tsukasa; Furuuchi, Toshinari; Miyaura, Norio; Suzuki, Akira

    Tetrahedron (1994), 50 (27), 7961-8CODEN: TETRAB; ISSN:0040-4020.

    Butadiene derivs. R1R2C:CR3CH:CH2 [R1 = R2 = H or Me, R1R2 = (CH2)5, R3 = aryl, 1-alkenyl, alkyl] were prepd. by palladium-catalyzed cross-coupling of butadienyl carbonates R1R2C:C:CHCH2OCO2Me with 9-alkyl-9-borabicyclo[3.3.1]nonanes (9-alkyl-9-BBN), 1-alkenylboronic acids, or arylboronic acids. The reaction proceeded regioselectively with palladium-phosphine complexes under neutral conditions.

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    (g) Djahanbini, D.; Cazes, B.; Gore, J. Reactive D’esters α-Alleniques. Synthese regiospecifique de diesters γ-alleniques et de dienes–1,3. Tetrahedron Lett. 1984, 25, 203– 206,  DOI: 10.1016/S0040-4039(00)99840-X

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    14g

    Reactivity of α-allenic esters. Regiospecific synthesis of γ-allenic diesters and 1,3-dienes

    Djahanbini, Dariouche; Cazes, Bernard; Gore, Jacques

    Tetrahedron Letters (1984), 25 (2), 203-6CODEN: TELEAY; ISSN:0040-4039.

    Pd(PPh3)4 catalyzed reaction of CH2(CO2Et)2 Na salt with RCR1:C:CHCHR2OAc and RCR1:C:CHCHR2OP(O)(OEt)2 (R, R1, R2 = H, Me) gave allenic malonates RCR1:C:CHCHR2CH(CO2Et)2 and (RCR1:C:CHCHR2)2C(CO2Et)2. Uncatalyzed reaction of R3MgBr (R3 = heptyl) with the same phosphates gave RCR1:CR3CH:CHR2 regiospecifically and with high stereoselectivity for the (Z)-isomer.

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15. 15

    (a) Kessler, S. N.; Hundemer, F.; Bäckvall, J.-E. A Synthesis of Substituted α-Allenols via Iron-Catalyzed Cross-Coupling of Propargyl Carboxylates with Grignard Reagents. ACS Catal. 2016, 6, 7448– 7451,  DOI: 10.1021/acscatal.6b02114

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    15a

    A Synthesis of Substituted α-Allenols via Iron-Catalyzed Cross-Coupling of Propargyl Carboxylates with Grignard Reagents

    Kessler, Simon N.; Hundemer, Fabian; Baeckvall, Jan-E.

    ACS Catalysis (2016), 6 (11), 7448-7451CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

    Propargyl acetates with homopropargylic or propargylic siloxy or methoxymethoxy groups (prepd. from ketones and protected terminal propargyl alcs. or from protected α-hydroxy aldehydes or ketones and terminal alkynes) such as PhCH2CH2CMe(OAc)C≡CCH2OTBDMS underwent chemoselective and regioselective coupling reactions with Grignard reagents in the presence of 1-5 mol% Fe(acac)3 under mild conditions (temp. -20°, 15 min reaction time) to give protected allenyl alcs. such as PhCH2CH2CMe:C:CRCH2OTBDMS (R = Me, Ph, PhCH2, PhCH2CH2CH2, Me3SiCH2, cyclohexyl, PhCMe2CH2, H2C:CHCH2CH2). Allenyl acetates were prepd. in one pot from (siloxymethyl)propargyl acetates and Grignard reagents by allenyl silyl ether formation followed by desilylation with TBAF and acetylation using Ac2O and DMAP; the allenyl acetates were prepd. on gram scale.

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    (b) Kessler, S. N.; Bäckvall, J.-E. Iron-catalyzed Cross-Coupling of Propargyl Carboxylates and Grignard Reagents: Synthesis of Substituted Allenes. Angew. Chem., Int. Ed. 2016, 55, 3734– 3738,  DOI: 10.1002/anie.201511139

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    15b

    Iron-catalyzed Cross-Coupling of Propargyl Carboxylates and Grignard Reagents: Synthesis of Substituted Allenes

    Kessler, Simon N.; Baeckvall, Jan-E.

    Angewandte Chemie, International Edition (2016), 55 (11), 3734-3738CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Presented herein is a mild, facile, and efficient iron-catalyzed synthesis of substituted allenes from propargyl carboxylates and Grignard reagents. Only 1-5 mol % of the inexpensive and environmentally benign [Fe(acac)3] at -20° was sufficient to afford a broad range of substituted allenes in excellent yields. The method tolerates a variety of functional groups.

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    (c) Posevins, D.; Bermejo-López, A.; Bäckvall, J.-E. Iron-Catalyzed Cross-Coupling of Propargyl Ethers with Grignard Reagents for the Synthesis of Functionalized Allenes and Allenols. Angew. Chem., Int. Ed. 2021, 60, 22178– 22183,  DOI: 10.1002/anie.202106742

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    15c

    Iron-Catalyzed Cross-Coupling of Propargyl Ethers with Grignard Reagents for the Synthesis of Functionalized Allenes and Allenols

    Posevins, Daniels; Bermejo-Lopez, Aitor; Backvall, Jan-E.

    Angewandte Chemie, International Edition (2021), 60 (41), 22178-22183CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Herein, an iron-catalyzed cross-coupling reaction of propargyl ethers RC≡CC(R1)(R2)OR3 (R = Me, n-Bu, cyclopropyl, Ph, etc.; R1 = Me, Et, CF2CF3, etc.; R2 = H, Ph, pyridin-3-yl, 1,3-dioxolan-2-ylmethyl, etc.; R1R2 = -(CH2)4-; R3 = Me, Ms, acetyl, methoxycarbonyl, etc.) with Grignard reagents R4MgX (R4 = Me, Cy, Ph, Bn, etc.; X = Br, Cl) was disclosed. The reaction was demonstrated to be stereospecific and allows for a facile prepn. of optically active allenes (R)/(S)-(R)/(S)-RC(R4)=C=C(R1)R2 via efficient chirality transfer. Various tri- and tetrasubstituted fluoroalkyl allenes RC(R4)=C=C(R1)R2 can be obtained in good to excellent yields. In addn., an iron-catalyzed cross-coupling of Grignard reagents with α-alkynyl oxetanes I (R5 = -pentyl, H, etc.; R6 = Et, Ph) and tetrahydrofurans II (R7 = Bu, cyclopropyl, etc; R8 = CF3, Me, etc.) is disclosed herein, which constitutes a straightforward approach towards fully substituted β- or γ-allenols.

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16. 16

    With phenyl or ethyl Grignard reagent, a complex mixture was obtained and the starting material 1a was completely decomposed. With dioxethyl Grignard reagent 2h, more than 94% of 1a was recovered.

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