By reaction of N-aryltrifluoroacetimidoyl chlorides with trialkyl phosphites the corresponding N-aryltrifluoroacetimidoylphosphonates CF3C(=NAr)P(O)(OR)(2) existing as dynamic equilibrium mixture of Z,Eisomers [Z/E similar to (7-12):1] were prepared. By F-19 NMR spectroscopy kinetic and activation parameters of Z-E isomerization were evaluated. Reaction of imidoylphosphonates with O-or S-centered nucleophiles leads to the products of addition to C=N bond whereas cycloaddition with of nitrile oxide gives previously unknown phosphorylated oxadiazolines.