On the stereoselectivity of glycosidation of thiocyanates, thioimidates, and thioglycosides.

Comparative side-by-side glycosylation studies demonstrated that glycosyl thiocyanates, thioimidates, and thioglycosides provide comparative stereoselectivities in glycosylations. Very high α-stereoselectivity that was previously recorded for glycosyl thiocyanates can be achieved, but only if glycosyl acceptors are equipped with electron-withdrawing acyl substituents. Partially benzylated glycosyl acceptors provided relatively modest stereoselectivity, which was on a par with other common glycosyl donors. Accordingly, thioimidates and thioglycosides showed high stereoselectivity similarly to that of thiocyanates with different classes of acylated primary and secondary glycosyl acceptors.