Methyl fucopyranoside undergoes highly regioselective 3-O-alkylation via complexation with phenylboronic acid, followed by treatment of the resulting 3,4-boronate with iodobutane in the presence of a tertiary amine and Ag 2 O. The essential step is suggested to be regioselective activation of the 3-O nucleophilic center upon amine coordination with the O-bonded boron atom.