Anomeric selectivity in the synthesis of galloyl esters of D-glucose.

The anomeric selectivity of the ester formation between d-glucopyranose and gallic acid was investigated under a variety of conditions. A new protocol was established that allows performing the reaction under conditions where mutarotation is very slow. Highly alpha- or beta-selective transformations are possible when starting with alpha- or beta-d-glucopyranose, respectively. Due to the kinetic anomeric effect, a high alpha-selectivity is more difficult to achieve than a high beta-selectivity. The new methodology presented in this article was compared with established procedures for the synthesis of gallotannins. In addition to the advantages of a high yield and an easy purification protocol, the new procedure uniquely allowed for a highly selective synthesis of alpha-products.