Enantioselective synthesis of α-bromo acid derivatives and bromohydrins from tartrate derived bromoacetals

Abstract

Bromination of the acetals 4 derived from aryl alkyl ketones, ArCOR, and (2R,3R)-tartaric acid results in bromoacetals 5 with 78–90% de. Hydrolysis of those compounds with Ar = 4-methoxyphenyl or 3-bromo-4-methoxyphenyl results, after recrystallisation, in α-bromoketones 8 with 66–98% ee which are shown to undergo the Baeyer–Villiger oxidation to α-bromoesters 9 with minimal racemisation. α-Bromoketone 8d is shown to undergo carbonyl reduction to threo-bromohydrin 15 with retention of stereochemistry.