Photochemical reactions of trialkylammonio-N-diphenylphosphinoylimides: rearrangement to N-phosphinoyl aminals and the formation of diphenylphosphinic amide

Abstract

The photolysis of the aminimide Ph₂P(O)N–NMe₃(1) in methanol gives the amide Ph₂P(O) NH₂ in high yield, but most of this is not formed from (1) directly via the nitrene; rather, it results from (solvolytic) decomposition of the phosphinoyl aminal Ph₂P(O)NHCH₂NMe₂(5) formed from (1) by a photochemical rearrangement. With Ph₂P(O)N–NEt₃ the corresponding rearrangement product Ph₂P(O)NHCHMeNEt₂(an ethylidene aminal) is not observed, but this is probably just a consequence of very rapid decomposition. Although substrates bearing both Me and Et groups on the ammonium N atom appear to form only the rearrangement product (a methylene aminal) that results from involvement of a Me group, the yield is reduced substantially relative to the yield of (5) from (1). The size of the reduction is consistent with an Et group participating in the rearrangement about twice as readily as a Me group, but the product (an ethylidene aminal) that results suffering (much) more rapid decomposition to Ph₂P(O)NH₂.