Multinuclear NMR structural study of novel γ-iminophosphonate and phosphine oxide derivatives

We report for the first time the synthesis of γ-iminophosphonates and phosphine oxides from the acid-catalysed reaction of primary amines with γ-phosphonylketones. The full characterization of these compounds through their 1H, 31P, and 13C NMR spectra indicates that they are obtained as a mixture of Z and E isomers. An unambiguous method for the assignment of these configurations, based on the 13C chemical shifts of C2 carbon atoms in the α position with respect to the C=N double bond is used. The 31P chemical shifts are also of diagnostic importance in assigning the Z and E configurations. Indeed, the phosphorus atom is found to resonate at a slightly higher field in Z isomers.