Treatment of methyl 5-deoxy-5-C-( diethoxyphosphinyl )-2,3-O-isopropylidene-beta-D- ri bofuranoside with sodium dihydrobis (2- methoxyethoxy ) aluminate , followed by hydrogen peroxide, mineral acid, and hydrogen peroxide, gave 5-deoxy-5-C-( hydroxyphosphinyl )-alpha,beta-D- ribopyranoses in 40-45% overall yield. The structures of these sugar analogs were effectively established on the basis of the mass and 400-MHz, 1H-n.m.r. spectra of the title compounds, derived by treatment with diazomethane and then acetic anhydride in pyridine.