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Asymmetric Synthesis of (S)-5,5,5,5′,5′,5′,5′-Hexafluoroleucine

✍ Scribed by Cong Zhang; Christian Ludin; Marcel K. Eberle; Helen Stoeckli-Evans; Reinhart Keese

Book ID: 102861506
Publisher: John Wiley and Sons
Year: 1998
Tongue: German
Weight: 572 KB
Volume: 81
Category: Article
ISSN: 0018-019X
DOI: 10.1002/hlca.19980810116

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✦ Synopsis

Abstract

(S)‐5,5,5,5′,5′,5′‐Hexafluoroleucine ((S)‐13) of 81 % ee is prepared from hexafluoroacetone (l) and ethyl bromopyruvate (= ethyl 2‐oxopropanoate) in 7 steps with an overall yield of 18% (Schemes 1 and 2). Key step in this sequence is the highly enantioselective reduction of the carbonyl group in α‐keto ester 4 either by bakers' yeast (91 % ee) or by ‘catecholborane’ 6 utilizing an oxazaborolidine catalyst, yielding hydroxy ester (R)‐5 with 99% ee. The absolute configuration was determined by X‐ray analysis of the HCl adduct (S,R)‐9b of (2__S__)‐N‐[(R)‐ l‐phenylethyl]‐5,5,5,5′,5′,5′‐hexafluoroleucine ethyl ester.

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