Reduction of N-acetyl-2-nitrodiphenylamines by triethyl phosphite: formation of dihydrophenazines involving a novel aromatic rearrangement.

2‐(Arylamino)aryliminophosphoranes from 2‐nitrodiarylamines

“…The authors tried to explain these results considering a function of hydrogen bond between both nitrogen atoms in the critical intermediates and implications of its absence. Quite different reaction course of triethyl phosphite with N ‐aryl‐2‐nitroacetanilide derivative has been reported by Maki et al . N ‐Arylbenzimidazole, formed via the aza‐Wittig cyclization of the triethyl phosphorimidate, was isolated in 3% yield, while the main product was N ‐acyldihydrophenazine, formed by intramolecular, multistep reaction of the intermediate nitrene with the aryl ring.…”

“…N ‐Arylbenzimidazole, formed via the aza‐Wittig cyclization of the triethyl phosphorimidate, was isolated in 3% yield, while the main product was N ‐acyldihydrophenazine, formed by intramolecular, multistep reaction of the intermediate nitrene with the aryl ring. As it was reported, the reaction of similar, although unacylated N ‐aryl‐2‐nitroaniline was complicated, and no defined product was isolated . However, N ‐phenyl‐2‐nitroaniline was reported to cyclize efficiently to afford phenazine when reacted with PPh 3 or (EtO) 3 P under microwave conditions .…”

“…As it was reported, the reaction of similar, although unacylated N-aryl-2-nitroaniline was complicated, and no defined product was isolated. [18] However, N-phenyl-2-nitroaniline was reported to cyclize efficiently to afford phenazine when reacted with PPh 3 or (EtO) 3 P under microwave conditions. [19] Unfortunately, all those reports did not put any light on the results described here.…”

“…The deoxygenation of nitroarenes has never become a practical method for the synthesis of aryliminophosphoranes because of its unpredictability and because other, much more general methods, such as the Staudinger reaction, have been developed. Deoxygenation of nitroarenes having o ‐amine group by trivalent phosphorus compounds has been reported to give varied results, providing phosphorimidates, dihydrophenazine derivatives, or phenazine …”

“…Łukasik and Wróbel synthesis of aryliminophosphoranes because of its unpredictability and because other, much more general methods, such as the Staudinger reaction, [17] have been developed. Deoxygenation of nitroarenes having o-amine group by trivalent phosphorus compounds has been reported to give varied results, providing phosphorimidates, [15] dihydrophenazine derivatives, [18] or phenazine. [19] Examples of isolated aryliminophosphoranes obtained that way from o-aminonitroarene derivatives are rare, [14,16] being rather exceptions from the major reaction course.…”