Utilization of Sugars in Organic Synthesis. Part 24. Regioselective Monotosylation of Non-Protected and Partially Protected Glycosides by the Dibutyltin Oxide Method.

Tosylation of non-protected glycopyranosides with p-toluenesulfonyl chloride in the presence of 4-dimethyl-aminopyridine, after activiation of the glycosides by dibutyltin oxide, gave mono-O-tosylates in good yield. The regioselectivity in this tosylation was different from that in the corresponding benzoylation for some glycosides. The reason for this difference is discussed based on an equilibrium of the tin intermediates and kinetic attack of the tosyl chloride on the intermediates. Thus, by application of this tosylation method to non-protected and partially protected glycosides, various glycoside mono-O-tosylates were synthesized regioselectively.