Palladium-Catalyzed Asymmetric Silaboration of Allenes

Toshimichi Ohmura, Hiroki Taniguchi, and Michinori Suginome*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan
J. Am. Chem. Soc., 2006, 128 (42), pp 13682–13683
DOI: 10.1021/ja063934h
Publication Date (Web): September 29, 2006
Copyright © 2006 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, suginome@sbchem.kyoto-u.ac.jp

Abstract

Abstract Image

An enantioselective silaboration of allenes was achieved using an achiral silylborane in the presence of a palladium catalyst bearing a chiral monodentate phosphine ligand. (R)-2-Bis(3,5-dimethylphenyl)phosphino-1,1‘-binaphthyl gave the highest enantioselectivities in the addition of (diphenylmethylsilyl)pinacolborane to the internal CC bond of terminal allenes at 0 °C, giving the corresponding β-borylallylsilanes in high yields with high enantiomeric excesses. The enantioselectivity depended on the bulkiness of substituents of allenes:  the enantiomeric excesses were found to be 91−93% ee (R = tert- and sec-alkyl), 88−90% ee (R = aryl), and 80−82% ee (R = prim-alkyl and Me) at 0 °C. Perfect chirality transfer was observed in the intramolecular cyclization reactions of the functionalized allylsilanes, affording highly enantioenriched cyclic alkenylboranes, which underwent Suzuki−Miyaura coupling with aryl halides.

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History

  • Published In Issue October 25, 2006
  • Received June 5, 2006

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