Photochemical rearrangement of dialkylphosphinic azides in methanol and other protic solvents

Abstract

On photolysis in methanol di-t-butylphosphinic azide (4; R = Bu^t) rearranges with loss of nitrogen to give methyl NP-di-t-butylphosphonamidate (6; R = Bu^t, X = OMe)(71%), presumably by way of a monomeric metaphosphonimidate (5; R = Bu^t) which is trapped by the solvent. Analogous rearrangements occur in other alcohols and in t-butylamine, although di-t-butylphosphinic amide is also a substantial product in ethanol and the major product in isopropyl alcohol. Di-isopropylphosphinic azide (4; R = Prⁱ) behaves in a similar way, but in methanol the less hindered diethylphosphinic azide (4; R = Et) suffers extensive solvolysis to methyl diethylphosphinate.