Synthesis of 2-(arylamino)ethyl phosphonic acids via the aza-Michael addition on diethyl vinylphosphonate

A simple way of synthesising 2-(arylamino)ethyl phosphonic esters and acids via the aza-Michael addition of amines to diethyl vinylphoshonate 'on water' was developed. Various 2-(arylamino)ethyl phosphonates were initially produced through the condensation of primary and secondary amines with diethyl vinylphosphonate, focussing on those bearing one aromatic moiety, giving generally good to high yields (i.e., 75-100%). These phosphonic esters were then hydrolysed in presence of bromomethylsilane to give quantitatively the corresponding phosphonic acids.