Reaction of sugar allylic mesylates with tri-n-butyltin cuprate affords the primary and secondary allyltinderivatives: Sug-CHCH-CH2SnBu3 and Sug-CH(SnBu3)-CHCH2 with the latter predominating. The SN2′ addition led almost exclusively to one isomer with the S configuration at the newly created stereogenic center. Only traces of the opposite R isomer were formed. Both stereoisomers of secondary allyltins