The reactions of diazomethane and dimethyloxo-sulfonium methylide with 1,2-dideoxy-4,5-O-isopropylidene-d-glycero-3-pentulose were studied. The sulfur ylide yielded two epimeric epoxides while diazomethane in addition furnished a homologous ketone. The reaction with diazomethane was carried out with varying concentrations of methanol in the reaction medium, and the relative yields of the three products