STEREOSELECTIVITY IN BENZYL 1,2-DIARYL ETHER CLEAVAGE BY BROMOTRIMETHYLSILANE

Lignin model benzyl 1,2-diaryl ether compounds such as 3- 4-hydroxy-3- methoxyphenyl)-2-(2-methoxyphenoxy)-3- (4-hydroxymethyl-2-methoxypheno xy) propanol are cleaved cleanly and selectively with bromotrimethylsi lane, anti-isomers producing anti-bromides with high (ca. 95%) diaster eoselectivity, presumably via anchimerically assisted displacement. Br omination of anti lignin model benzyl alcohols proceeds with 85% reten tion of configuration when other hydroxy groups in the molecule are pr otected, and ca. 75% retention when they are free. In both ether-cleav ages and brominations, syn-isomers show notably lower stereoselectivit y with marginal inversion.