Dehydroxy substitution reactions of the anomeric hydroxy groups in some protected sugars initiated by anodic oxidation of triphenylphosphine

Abstract

The anodic transformation of 2,3:5,6-di-O-isopropylidene-α-D- mannofuranose (4) and 2,3,4,6-tetra-O-benzyl-D-glucopyranose (5) to the corresponding alkoxy phosphonium ions induces dehydroxy substitution of the sugars at the anomeric positions. Their dehydroxy fluorination and chlorination has been achieved by constant-current electrolysis with CH2Cl2-1,2-dimethoxyethane/Ph3P/Ph3PH·BF4 and with CH2Cl2/Ph3/Et4N·Cl, respectively. The electrolysis in the presence of Ph3P has proved to serve O-glycosylation with 4 or 5 as a glycosyl donor, provided that an aliphatic alcohol as a glycosyl acceptor is a weaker nucleophile, such as (CF3)2CHOH, CF3CH2OH, and tert-BuOH, than the protected sugar toward Ph3P(+·) generated anodically from Ph3P. The present electrochemical reactions for 2,3,4,6-tetra-O-acetyl-D-glucopyranose were unsuccessful, except for the dehydroxy chlorination.