Phase-transfer-catalyzed asymmetric glycolate alkylation.

Abstract

[reaction: see text] Asymmetric surrogate glycolate alkylation has been performed under phase-transfer conditions. Diphenylmethyloxy-2,5-dimethoxyacetophenone with trifluorobenzyl cinchonidinium catalyst and cesium hydroxide provided alkylation products at -35 degrees C in high yield (80-99%) and with excellent enantioselectivities (90:10 to 95:5). Useful alpha-hydroxy products were obtained using bis-TMS peroxide Baeyer-Villiger conditions and selective transesterification. The intermediate aryl ester can be obtained with >99% ee after a single recrystallization. A tight ion-pair model for the observed (S)-stereoinduction is proposed.