Effective induction of beta-selectivity using alpha-OR beta-mannosyl 6-nitro-2-benzothiazoate in mannosylation

摘要

High beta-selective mannosylations of glycosyl acceptors with an alpha-mannosyl 6-nitro-2-benzothiazoate donor (1alpha) were carried out smoothly in the presence of a catalytic amount of tetrakis(pentafluorophenyl)boric acid [HB(C_6F_5)_4] to afford the corresponding disaccharides in good to high yields:it was proved that high beta-selectivity was entirely dependent on the characteristic properties of a donor (1alpha) and a catalyst HB(C_6F_5)_4.Interestingly,it was observed that in situ anomerization from 1beta and 1alpha took place rapidly when beta-mannosyl donor (1beta) was treated with a catalytic amount of HB(C_6F_5)_4 in CH_2Cl_2.