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Solution Structures of Lithium Enolates of Cyclopentanone, Cyclohexanone, Acetophenones, and Benzyl Ketones. Triple Ions and Higher Lithiate Complexes
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Section:Abstract
Multinuclear NMR spectroscopic studies at low temperature (−110 to −150 °C) revealed that lithium p-fluorophenolate and the lithium enolates of cyclohexanone, cyclopentanone and 4-fluoroacetophenone have tetrameric structures in THF/Et2O and THF/Et2O−HMPA by study of the effects of the addition of HMPA. The Z and E isomers of the lithium enolate of 1,3-bis-(4-fluorophenyl)-2-propanone (5F-Li) show divergent behavior. The Z isomer is completely dimeric in pure diethyl ether, and mostly dimeric in 3:2 THF/ether, where monomer could be detected in small amounts. TMTAN and PMDTA convert Z-5F-Li to a monomeric amine complex, and HMPA converts it partially to monomers, and partially to lithiate species (RO)2Li− and (RO)3Li2−. Better characterized solutions of these lithiates were prepared by addition of phosphazenium enolates (using P4-tBu base) to the lithium enolate in 1:1 ratio to form triple ion (RO)2Li− P4H+, or 2:1 ratio to form the higher lithiate (RO)3Li2− (P4H+)2) (quadruple ions). The E isomer of 5F-Li is also dimeric in 3:2 THF/Et2O solution, but is not detectably converted to monomer either by PMDTA or HMPA. In contrast to Z-5F-Li, the E isomer is tetrameric in diethyl ether even in the presence of excess HMPA. Thus for the two isomers of 5F six different enolate structures were characterized: tetramer, dimer, CIP-monomer, SIP-monomer, triple ion, and quadruple ion.
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This article has been cited by 3 ACS Journal articles (3 most recent appear below).
Mechanistic Studies of the Lithium Enolate of 4-Fluoroacetophenone: Rapid-Injection NMR Study of Enolate Formation, Dynamics, and Aldol Reactivity
Kristopher J. Kolonko, Daniel J. Wherritt, and Hans J. ReichJournal of the American Chemical Society2011 133 (42), 16774-16777Mechanistic Studies of the Lithium Enolate of 4-Fluoroacetophenone: Rapid-Injection NMR Study of Enolate Formation, Dynamics, and Aldol Reactivity
Kristopher J. Kolonko, Daniel J. Wherritt, and Hans J. ReichJournal of the American Chemical Society2011 133 (42), 16774-16777Lithium enolates are widely used nucleophiles with a complicated and only partially understood solution chemistry. Deprotonation of 4-fluoroacetophenone in THF with lithium diisopropylamide occurs through direct reaction of the amide dimer to yield a ...
On the Nature of the Oxidative Heterocoupling of Lithium Enolates
Brian M. Casey and Robert A. Flowers, IIJournal of the American Chemical Society2011 133 (30), 11492-11495On the Nature of the Oxidative Heterocoupling of Lithium Enolates
Brian M. Casey and Robert A. Flowers, IIJournal of the American Chemical Society2011 133 (30), 11492-11495The coupling of enolates through single-electron oxidation is one of the most direct routes for generating 1,4-dicarbonyls. Recent work on the intermolecular heterocoupling of equimolar amounts of two different enolates through single-electron oxidation ...
Structure and Dynamics of α-Aryl Amide and Ketone Enolates: THF, PMDTA, TMTAN, HMPA, and Crypt-Solvated Lithium Enolates, and Comparison with Phosphazenium Analogues
Kristopher J. Kolonko, Ilia A. Guzei, and Hans J. ReichThe Journal of Organic Chemistry2010 75 (18), 6163-6172Structure and Dynamics of α-Aryl Amide and Ketone Enolates: THF, PMDTA, TMTAN, HMPA, and Crypt-Solvated Lithium Enolates, and Comparison with Phosphazenium Analogues
Kristopher J. Kolonko, Ilia A. Guzei, and Hans J. ReichThe Journal of Organic Chemistry2010 75 (18), 6163-6172A variety of multinuclear NMR techniques, in combination with X-ray diffraction methods, were used to probe the solution structure of α-aryl lithium enolates of bis(4-fluorobenzyl) ketone (1-H), phenyl 4-fluorobenzyl ketone (2-H), and N,N-dimethyl 4-...
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History
- Published In Issue August 19, 2009
- Article ASAPJuly 27, 2009
- Received: April 29, 2009
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