Chiral Carbanions, Part 4: [1] Borylation of (Trimethylsilyl)methyl N,N-Dialkylcarbamates - Diastereoselectivity and Structural Studies

Abstract

(Trimethylsilyl)methyl carbamates were prepared from (trimethylsilyl)methanol and N,N-dialkylcarbamoyl chlorides and were metalated by s-BuLi/TMEDA. The configurationally labile lithiated carbamates were reacted with borates derived from (+)-pinane-2,3-diol to give boronates diastereoselectively (yields up to 84%, dr up to 17:1). The absolute configurations at the boron-bearing carbon atoms of three boronates were assigned by single crystal X-ray structure analyses.

Key words

carbamates - carbanions - lithiation - nucleophilic substitution - diastereoselectivity

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The structural data of compounds 10, 12c and 13b have been deposited at the Cambridge Crystallographic Data Centre under the reference numbers CCDC 239224, 239226, 239225, respectively. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: [phone]; e-mail: [e-mail]].