A new approach to the synthesis of methylene exo-glycalsis described. Oxidation of glycosylthiolmethyl chloride(GTM-Cl) with mCPBA afforded the corresponding glycosylchloromethyl sulfone in almost quantitative yield, whichunderwent KOtBu-induced Ramberg−Bäcklund rearrangement to furnish the desired methylene exo-glycal in excellentyield.