Anchimeric assistance by the anomeric phenylthio group in the nucleophilic substitution of a 6-O-trifluoromethanesulfonyl-β-d-galactopyranoside

Nucleophilic displacement by the cyanide anion of the 6-O-triflyl group in phenyl 6-O-triflyl-2,3-di-O-benzyl-4-O-p-methoxybenzyl-1-thio-β-d-galactopyranoside takes place via an intermediate 1,6-sulfonium salt resulting from the anchimeric assistance of the C-1 phenylthio group.