1-Dimethylamino-1-methoxy-1-alkenes (ketene O, N-acetals), 1-dimethylamino-1-ethylthio-1- alkenes (ketene S, N-acetals) and 1, 1-bis (dimethylamino) ethylene (ketene N, N-acetal) reacted with diethyl phosphite to give the corresponding (E)-diethyl 1-dimethylamino-1- alkenylphosphonates. Although ketene diethylacetal (ketene O, O-acetal) reacted with diethyl phosphite to give diethyl 1, 1-diethoxy-1-ethylphosphonate, 1, 1-bis (ethylthio)-1- ...