Glycosyl Phosphonium Halide as a Reactive Intermediate in Highly α-Selective Glycosylation

Abstract

Abstract Highly α-selective glycosylations of several glycosyl acceptors with 2,3,4,6-tetra-O-benzyl-d-glucopyranosyl bromide (4) proceeded smoothly in the presence of tri(1-pyrrolidino)phosphine oxide in CH2Cl2 at room temperature or in refluxing CHCl3 via glycosyl phosphonium bromide intermediates and the corresponding disaccharides were afforded in good yields with high selectivities. Further, the one-pot glycosylation starting from glycosyl acetate using iodotrimethylsilane and phosphine oxide also proceeded efficiently in CH2Cl2 at room temperature to give the corresponding disaccharides, although this one-pot synthesis of α-glycoside via in situ anomerization procedure is considered difficult because glycosyl halide reacts with trimethylsilyl acetate easily to regenerate glycosyl acetate, a starting glycosyl donor.