Commercially available “glyoxal trimer dihydrate” was converted into monomeric anhydrous glyoxal which was allowed to react with trimethyl phosphite to form 2,2,2-trimethoxy-2,2-dihydro-1,3,2-dioxaphospholene. The phospholene was transformed into dimethyl 2-oxoethyl phosphate (“diose phosphate”) by anhydrous HCI, and into a series of α-hydroxy β-keto aldehyde phosphates by carboxylic acid chlorides. The reaction of the phospholene with phosgene, COCl2, gave dimethyl phosphohydroxymalonaldehyde chloride. The 31P and 1H nmr and infrared spectra were studied. © 1969, American Chemical Society. All rights reserved.