Anomeric O ‐Alkylation, 9. Disaccharide Synthesis via Anomeric O ‐Alkylation

Base‐promoted reaction of tetra‐ O ‐benzyl‐glucose 1a with secondary alkyl trifluoromethanesulfonates 2 and 3 in toluene provides in the presence of 15‐crown‐5 preferentially β‐glycosides 2aβ and 3aβ , respectively, in high yields. For reactions carried out at lower temperatures and with trifluoromethanesulfonates derived from secondary hydroxy groups of sugars aprotic dipolar solvents (HMPT/DMF, HMPT/THF) are required. Thus, treatment of 1‐ O ‐unprotected hexoses 1a – e with trifluoromethanesulfonates 4 , 6 , and 7 affords the corresponding (1→4)‐connected disaccharides 4a – e and the (1→3)‐connected disaccharides 6b and 7b , respectively, in high yields. Under these conditions the α:β ratio of the products resembled the anomeric ratio of the starting material.