Stereoselective α-Glucosylation with Tetra-O-benzyl-α- d -glucose and a Mixture of Trimethylsilyl Bromide, Cobalt(II) Bromide, Tetrabutylammonium Bromide, and a Molecular Sieve. A Synthesis of 3,6-Di-O-(α- d -glucopyranosyl)- d -glucose

A mixture of trimethylsilyl bromide, cobalt(II) bromide, tetrabutylammonium bromide, and a molecular sieve (4A) is effective for the stereoselective, one-stage α-glucosylation of alcohol with 2,3,4,6-tetra-O-benzyl-α-d-glucopyranose in dichloromethane. Using this procedure, several disaccharide derivatives as well as O-α-d-glucopyranosyl-(1→3)]-O-[α-d-glucopyranosyl-(1→6)]-d-glucopyranose are synthesized.