The synthesis of dimethyl 6-O-acetyl-2,3-anhydro-a-D- mannopyranosylphosphonates and the corresponding a- and ߭ allo derivatives is described. Dimethyl 4,6-di-O-acetyl-2,3-dideoxy-D-erythro-hex-2-enopyranosylphosphonates, although unreactive towards normal epoxidizing agents (3-chloroperoxybenzoic acid, trifluoroperoxyacetic acid, etc), underwent smooth epoxidation with hydrogen peroxide in the presence of sodium tungstate or dodecatungstophosphoric acid. An interesting regiospecific deacetylation of the 4-acetate occurred under these conditions. The structures of these anhydro glycosyl phosphonates were determined by 1H and 13C n.m.r. spectroscopy, and confirmed by X ray structural analysis in the case of dimethyl 6-O-acetyl-2,3-anhydro-a-D-mannopyranosylphosphonate , and of dimethyl 6-O-acetyl-2,3-anhydro-߭D-allopyranosylphosphonate.