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.