Synthesis of a 2H‐Azirine by [1 + 2] Cycloaddition of a Phosphinocarbene with a Nitrile and Its Ring‐Expansion to a 1,2λ5‐Azaphosphete

A new type of carbene reaction is observed with the stable phosphinocarbene 1. It reacts with benzonitrile to give the 2H-azirine 2, which in dichloromethane is converted into the 1,2λ5-azaphosphete 3 after addition of a catalytic amount of dichloro(p-cymene)ruthenium(II). R = (c-C6H11)2N.