Stereoselectivity in benzyl 1, 2-diaryl ether cleavage by bromotrimethylsilane

Abstract

Lignin model benzyl 1, 2-diaryl ether compounds such as 3-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-3-(4-hydroxymethyl-2-methoxyphenoxy)propanol are cleaved cleanly and selectively with bromotrimethylsilane, anti-isomers producing anti-bromides with high (ca. 95%) diastereoselectivity, presumably via anchimerically assisted displacement. Bromination of anti lignin model benzyl alcohols proceeds with 85% retention of configuration when other hydroxy groups in the molecule are protected, and ca. 75% retention when they are free. In both ether-cleavages and brominations, syn-isomers show notably lower stereoselectivity with marginal inversion.