Reactions of diastereomeric 2,4,5-triphenyl-1,3-dioxolans with N-bromosuccinimide and t-butyl perbenzoate

Abstract

Two diastereomeric 2,4,5-triphenyl-1,3-dioxolans isolated from the acetalization of meso-hydrobenzoin with benzaldehyde have been assigned their respective configurations based on spectroscopic evidence. The reactions of r-2,c-4,t-5-triphenyl-1,3-dioxolan (4) with N-bromosuccinimide and with t-butyl perbenzoate catalysed by cuprous chloride have been shown to give erythro-1-benzoyloxy-2-bromo-1,2-diphenylethane and meso-hydrobenzoin dibenzoate respectively. The corresponding reactions of r-2,c-,.c-5-triphenyl-1,3-dioxolan (5) and r-2, t-4, t-5-triphenyl-1,3-dioxolan (6), on the other hand, gave threo-1-benzoyloxy-2-bromo-1,2-diphenylethane and (±)-hydrobenzoin dibenzoate respectively. These stereospecific results are consistent with SN2 ring opening involving a dioxolenyl cation.