A novel and convenient synthesis of diethyl [nitro(diazo)methyl]phosphonate and its reactions with various alkenes are described. The reactivity of diethyl [nitro(diazo)methyl]phosphonate is shown to be dependent on the structure of the alkene. A number of cyclopropyl α-nitrophosphonates were obtained. diazo compounds - phosphonates - alkenes - cyclopropanation - carbenes