An efficient synthesis of new 1′-C-methyl-α-O-disaccharides using 1-methylenesugars as the glycosyl donors

A series of new 1′-C-methyl-α-disaccharides were firstly synthesized by the directly Lewis acid-catalyzed O-glycosidation of 1-methylenesugars used as glycosyl donors. The O-glycosidation afforded stereospecifically the corresponding 1′-methyl-α-O-glycosides whose configurations were tentatively assigned by the NMR spectra, COSY and the C–H coupling constant 3JH−2′,Me−1′. The O-glycosidation of the acetyl protected 1-methylenesugars showed that the acetyl group at the C-2-O position was not effective to control the stereochemistry of the product by neighboring group participation because of the formation of a tertiary oxycarbenium ion as a stable intermediate.