Stereospecific Synthesis of 1,2-<i>trans</i>-1-Phenylthio-β-D-Disaccharides Under Phase Transfer Catalysis

Abstract

Peracetylated α-glycobiosyl bromides 1-5 derived from commercially available disaccharides, were transformed with complete anomeric stereocontrol into phenyl 1,2-trans-1-thio-β-D-glycobiosides 6-10 by nucleophilic displacement under phase transfer catalyzed glycosidation in 77-92% yields. The reaction proceed rapidly for most bromides in dichloromethane, but failed under similar conditions, to provide complete conversion of the melibiosyl bromide 4 into the S-phenyl thioglycoside 9. Nevertheless, the reaction gave good results when performed in toluene or ethyl acetate.