Kinetic resolution of α-acetoxy carboxylic acids with homochiral superQuats

S.P. Bew, S.G. Davies, S.-I. Fukuzawa

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16 Citations (Scopus)

Abstract

Preliminary investigations focused on the kinetic resolution of (±)-α- acetoxy mandelic carboxylic acid chloride with isopropyl SuperQuat and isopropyl Evans' homochiral auxiliaries. The addition of 2 equiv. of the acid chloride to the lithium salts of the auxiliaries (SuperQuat and Evans') at - 100°C in the THF afforded the corresponding N-acyl auxiliaries in high chemical yields (95% and 89%) and d.e.'s of 66% and 40%, respectively. Using the same mandelic acid chloride but incorporating SuperQuat auxiliaries derived from (S)-phenylglycine and (S)-phenylalanine yielded the corresponding N-acyl SuperQuats in 86% and 90% and d.e.'s of 66% and 30%, respectively. Substituting the phenyl group within the α-acetoxy mandelic acid chloride for a n-butyl, tert-butyl and cyclohexyl group changed the d.e. significantly when kinetically resolved with isopropyl SuperQuat. The yields were all similar, i.e., ~90% but the d.e.'s varied considerably, with values of 20%, 50%, and 82%, respectively. Attempted kinetic resolution of α- methoxyphenylacetyl chloride using the lithium salt of isopropyl SuperQuat revealed a diasteroselectivity of 45%, significantly lower than that obtained with the corresponding α-acetoxy carboxylic acid chlorides. (C) 2000 Wiley- Liss, Inc.
Original languageEnglish
Pages (from-to)483-487
Number of pages5
JournalChirality
Volume12
Issue number5-6
Publication statusPublished - 1 Jan 2000

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