An efficient synthesis of new 1'-C-methyl-#alpha#-disaccharides using 1-methylenesugars as the glycosyl donors

摘要

A series of new 1'-C-methyl-#alpha#-disaccharids 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-#alpha#-O-glycosides whose configurations were tentatively assigned by the NMR spectra,COSY and the C-H coupling constant ~3J_(H-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 tertiaryo oxycarbenium ion as a stable intermediate.