The synthesis of α-iminophosphonates derived from ketones has been achieved by aza-Wittig reaction of P-trimethylphosphazenes with acylphosphonates. These unstable compounds can be used for the synthesis of chiral α-aminophosphonate derivatives through addition of nucleophiles to the C-N iminic double bond. Moreover, if α,β-unsaturated imines are used, regioselective Michael addition to the conjugated bond yields α-dehydroamino-phosphonic acid derivatives functionalized at the γ-position.