α-Carbamoyl phosphonates are useful reagents for the Horner-Wadsworth-Emmons olefination of aldehydes en route to medicinally relevant polysubstituted acrylamides. A new synthetic approach to these reagents has been developed. The methodology relies on the microwave-promoted Wolff rearrangement of α-acyl-α-diazophosphonates with trapping of the ketene intermediate in situ with various amines.