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Synlett 2011(2): 177-180  
DOI: 10.1055/s-0030-1259282
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

New Potentially Chelating Chiral Magnesium Amide Bases for Use in Enantioselective Deprotonation Reactions

William J. Kerr*, Michael Middleditch, Allan J. B. Watson
Department of Pure and Applied Chemistry, WestCHEM, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK
Fax: +44(141)5484246; e-Mail: w.kerr@strath.ac.uk;
Further Information

Publication History

Received 12 November 2010
Publication Date:
23 December 2010 (online)

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Abstract

A series of chiral secondary amines, incorporating a five- or six-membered heterocycle, were synthesised and used to prepare novel chiral magnesium bisamide reagents. These amide bases were subsequently applied within asymmetric deprotonation reactions to probe the potential for chelation-assisted selectivity enhancement. Good levels of selectivity could be achieved [up to 87:13 er (R/S)] across a range of prochiral cyclohexanone substrates when employing a thiophene-derived magnesium bisamide complex.

Key words

asymmetric synthesis - enantioselectivity - heterocycles - enolate - magnesium

    References and Notes

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3

Commercially available from Aldrich Chemical Co., CAS# [38235-77-7], catalogue no. 431737.

5

Commercially available from BASF SE (ChiPros®) (http://www.intermediates.basf.com/en/intermed/products/chipros/amines/) or the Aldrich Chemical Co.: (R)-1-phenylethyl-amine CAS# [3886-69-9]; and (S)-1-phenylethylamine CAS# [2627-86-3].

7

Due to limited availability of (R)-phenylethylamine during the course of this study, we were compelled to use the more readily obtainable S-enantiomer for the preparation of several of the desired chiral amines.

10

Commercially available from Aldrich Chemical Co., CAS# [1191-47-5].