Regioselective debenzylation of C-glycosyl compounds by boron trichloride

Boron trichloride has been found to promote selective deprotection of 1,2- or 1,3-cis oriented secondary benzyl ethers of per-benzylated C-glycosyl derivatives. The reactivity towards BCl3 follows the order: C-4 ⩾ C-2 > C-6 > C-3 for C-glucopyranosyl derivatives and C-3 ⩾ C-4 > C-6 > C-2 for C-galactopyranosyl derivatives. Preparatively useful selective debenzylation at secondary positions was possible after careful control of reaction conditions.