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

Abstract

2-Phenyl-3-phenylimino-3H-indole N-oxide (an indolic nitrone) reacts with triethyl and triisopropyl phosphite in refluxing xylene and tert-butylbenzene 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 starting nitrone and in part from the interaction of the indolenine with phosphites. The formation of the products arising from the reduction of the indolenine is explained by an electron transfer process between this intermediate and the phosphite; whereas the formation of the phosphorylated products is interpreted through the evolution of the intermediate zwitterion generated by the nucleophilic attack of the phosphite on carbon- 2 of the indolenine. The formation of this intermediate is also discussed in terms of an electron transfer process. Crystal structures of 1-diethylphosphoryl-2-phenyl-3-phenylamino-1H-indole and 2-phenyl-4-phenylimino-4H-3,1-benzoxazine are also described.