Lifetime of the glucosyl oxocarbenium ion and stereoselectivity in the glycosidation of phenols with 1,2-anhydro-3,4,6-tri-O-methyl-α-D-glucopyranose

Article abstract of DOI:10.1016/S0040-4020(97)00660-1

The glycosidation of para substitued phenols with 1,2-anhydro-3,4,6-tri-O-methyl-α-D-glucopyranose. ZnCl₂ catalyzed, gives predominatly the corresponding α-anomers. In the presence of an amino base, 1,1,3,3-tetramethylguanidine, however, enhances the β-selectivity, which becomes practically complete when tile reaction is carried out under basic conditions, by addition of K₂CO₃ and 18-crown-6. A rationaliation based on the lifetime of the oxocarbenium ion intermediate and on the nucleophilicity of the phenols is proposed.