o-Nitroaniline derivatives. Part V. Cyclisation of N-acylated derivatives of N-benzyl- and N-p-nitrobenzyl-o-nitroaniline: a comparison of carboxamides and sulphonamides

Abstract

The N-acetyl and N-benzoyl derivatives of N-benzyl- and N-p-nitrobenzyl-o-nitroaniline are cyclised, by sodium methoxide in methanol, to 2-aryl-1-hydroxybenzimidazoles; however, in the corresponding reactions of the N-methylsulphonyl and N-p-tolylsulphonyl derivatives, cyclisation occurs only in the case of the p-nitrobenzyl compounds. Cyclisation of the N-benzyl-o-nitroaniline derivatives apparently involves deacylation as the first step, whereas kinetic evidence indicates that deacylation follows cyclisation in the reactions of the N-p-nitrobenzyl-o-nitroaniline derivatives. N-Ethoxycarbonyl-N-p-nitrobenzyl-o-nitroaniline is similarly cyclised by sodium ethoxide in ethanol. In the preparation of this compound, from ethyl N-o-nitrophenylcarbamate and p-nitrobenzyl bromide, 1-p-nitrobenzyloxy-2-p-nitrophenylbenzimidazole is obtained as a by-product.The non-equivalence of the benzylic protons in the n.m.r. spectra of the title compounds is discussed.