1-O-Alkylation of D-Glucopyranose

Direct 1-O-methylation of 1-O-metalated 2,3,4,6-tetra-O-benzyl-d-glucose (1) with methyl trifluoromethanesulfonate (3a) as a strong alkylating agent led to the methyl gluco-pyranosides 4a with the α/β anomer ratios varying from 4:1 to 1:11 depending on solvent and temperature. With the less electrophilic trifluoromethanesulfonates of d-glucose 3b and 3c, of d-ribose 3d, and d-glycerol (3e) as alkylating agents, 1 gave the β-disaccharides and β-glycosides 4b-β 4e-β, exclusively. Product formation is discussed in terms of the various nucleophilicities of the starting materials and in terms of different internal complexation. Introduction of the sterically demanding (p-methoxyphenyl)diphenyl-methyl protecting group in 6-O-position of 2,3,4-tri-O-ben-zyl-D-glucose to form 8 and subsequent 1-O-metalation and reaction with trifluoromethanesulfonate 3c gave the α-con-nected isomaltoside 9C-α. However, from 1-O-metalated 8 and the trifluoromethanesulfonates of glycerol 3e and 3f under identical reaction conditions, only the β-connected glycosides 9e-β and 9f-β, respectively, were obtained. Structures were assigned by 1H NMR and by deprotection to known compounds.