α-Selective Glucosylation Can Be Achieved with 6- O - para -Nitrobenzoyl Protection.

A systematic study of the effect of various 6--acyl groups on anomeric selectivity in glucosylations with thioglycoside donors was conducted. All eight different esters were found to induce moderate-to-high α-selectivity in glucosylation with l-menthol with the best being 6---nitrobenzoyl. The effect appears to be general across various glucosyl acceptors, glucosyl donor types, and modes of activation. No evidence was found in favor of distal participation.