New insights on the reaction of trialkyl phosphites with 2-phenyl-3-phenylimino-3H-indole N-oxide: an indolic nitrone. Crystal structures of 1-diethylphosphoryl-2-phenyl-3-phenylamino-1H-indole and 2-phenyl-4-phenylimino-4H-3,1-benzoxazine

2-Phenyl-3-phenylimino-3H-indole N-oxide (an indolic nitrone) reacts with t riethyl and triisopropyl phosphite in refluxing xylene and tert-butylbenzen e to give 2-phenyl-3-phenylimino-3H-indole (indolenine) in very good yield. The same reaction carried out in refluxing phosphite gave rise to a series of compounds which in part derive from the thermal rearrangement of the st arting nitrone and in part from the interaction of the indolenine with phos phites. The formation of the products arising from the reduction of the ind olenine is explained by an electron transfer process between this intermedi ate and the phosphite; whereas the formation of the phosphorylated products is interpreted through the evolution of the intermediate zwitterion genera ted by the nucleophilic attack of the phosphite on carbon-2 of the indoleni ne. The formation of this intermediate is also discussed in terms of an ele ctron transfer process. Crystal structures of 1-diethylphosphoryl-2-phenyl- 3-phenylamino-1H-indole and 2-phenyl-4-phenylimino-4H-3,1-benzoxazine are a lso described.