Reduction of nitro- and nitroso-compounds by tervalent phosphorus reagents. Part VIII. Syntheses of benzimidazoles and anthranils

Abstract

Reactions of triethyl phosphine with N-benzylidene-2-nitroaniline and its 4-methyl-2-nitroaniline analogue in boiling t-butylbenzene give the corresponding 2-phenylbenzimidazoles in moderate yields. Similar treatment of 2′-nitrobenzanilide, on the other hand, gives 2-phenylbenzimidazole in only 3% yield. 2-Nitrobenzophenone, 2′-nitrochalcone, and 5-chloro-2-nitroacetophenone, when treated with undiluted triethyl phosphite, give the corresponding anthranils (2,1-benzisoxazoles) in moderate yields. 2-Nitroacetophenone and ethyl 2-nitrobenzoate under these conditions do not undergo detectable cyclisation but give the corresponding amines and phosphoramidates.