Zwitterionic Phosphoranides as Intermediates in the Reaction of Phosphorus Tribromide with N,N-Dimethyl-N′-arylformamidines

ABSTRACT Cyclic zwitterionic phosphoranides 2a,b were found to be intermediate products in the reaction of N,N‐dimethyl‐N′‐(aryl)formamidines with PBr3. The structure of phosphoranide 2a was determined by means of the X‐ray and quantum chemistry investigations. Mechanism of its formation was proposed based on Density functional theory (DFT) calculations. Reactions of 2 with amines and selenium yielded either C‐phosphorylated formamidines or benzazaphospholes. The first example of intramolecular heterocyclization of a pentavalent phosphorus derivative 15b into 3Н‐1,3‐benzazaphosphole has been demonstrated.