Regioselective Glycosylation of Unprotected Methyl Hexopyranoside by Transient Masking with Arylboronic Acid

Unprotected methyl !/"-D-galactopyranoside, !/"-D-glucopyranoside, !-L-fucopyranoside, and !-L-rhamnopyranoside were regioselectively glycosylated by treatment with per-O-pivaloyl-!-D-glycopyranosyl bromide to give glycosyl-"(1!3)-galactopyranoside,glycosyl-"(1!2/3)-glucopyranoside, glycosyl-"(1!2)-fucopyranoside, and glycosyl-"(1!4)-rhamnopyranoside,respectively.The reaction mainly occurred at the secondary hydroxy group, even in the presence of a primary hydroxy group, which was masked with arylboronic acid.