Reactions of bromonitroalkenes with tervalent phosphorus. Part II. Reaction in methanol

Abstract

The reactions of β-bromo-β-nitrostyrenes with triphenylphosphine in methanol have been investigated with a view to obtaining evidence for the site of initial attack. Some ion-pair hydrolysis products were obtained, but the major products from 2-phenyl- and 2-(4-methylphenyl)-1-bromo-1-nitroethylene were the novel rearranged benzylideneaminomethylphosphonium salts (7a and b), which were identified both from their spectra and by chemical degradation. With β-bromo-β-nitrostyrenes containing electron-withdrawing groups, triphenyl(triphenylphosphoranylideneamino)phosphonium bromide and α-formyl-α-phosphoniobenzylides were obtained; similar products were formed in the reaction of 1-chloro-2-nitrophenylethylene, and for this reason a common intermediate is proposed. Both azirine and oxaziridine intermediates are suggested to explain the formation of the foregoing products; the results of reactions in methan[²H]ol support one of the proposed mechanisms.