Regio- and stereoselective glycosylation of 1,2-O-unprotected sugars using organoboron catalysts

Three different types of organoboron-catalyzed glycosylations using 1,2-O-unprotected sugars have been developed for the synthesis of 1,2-cis-glycosides. Although arylboronic acid-catalyzed dehydrative coupling with glycosyl acceptors provides the thermodynamically controlled products as a mixture of two isomers, diarylborinic acid-catalyzed O-alkylation with O-triflyl sugars gave the desired 1,2-cisglycosides in a highly stereoselective manner. Furthermore, tricyclic borinate complexes consisted of 1,2-glycosyl diols and diarylborinic acids efficiently promote the O-glycosylation with glycosyl phosphites and anhydrosugars, leading to 1,1'-beta,alpha- and alpha,alpha-trehaloses, respectively. In each case, tricyclic 9-oxa-10-boraanthracene-derived borinic acid bearing a dimethyl or bis-trifluoromethyl group exhibits the best catalytic performance for the regio- and stereoselective glycosylation. (C) 2020 Elsevier Ltd. All rights reserved.