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12.4.4.6 Rearrangement of Substituents

DOI: 10.1055/sos-SD-012-00657

Grimmett, M. R.Science of Synthesis, (200212601.

The photo-Fries rearrangement of 1-acyl- or 1-aroyl-1H-benzimidazol-2(3H)-ones 117 in benzene or ethanol solutions results in some deacylation, but also forms 4- 118 and 5-acyl products 115. The initial N-acyl substrates are formed by photolysis or thermolysis of 2-acylbenzimidazole 1-oxides 116 (Scheme 57).[‌484‌] The initial photorearrangement to the benzimidazolone also occurs with benzimidazole N-oxides and may involve displacement of an alkyl group from the 2-position to an annular nitrogen, e.g. 1-benzyl-2-ethyl-1H-benzimidazole 3-oxide gives 1-benzyl-3-ethyl-1H-benzimidazol-2(3H)-one as the major rearrangement product.[‌485‌] This reaction has similarities to the effects of tosyl chloride in the presence of hydroxide ions on 2,3-(polymethylene)benzimidazole 1-oxide, which rearranges to a 1,3-(polymethylene)benzimidazolone.[‌486‌] At 150°C in the absence of light, 2-(aryloxy)benzimidazoles are photolyzed with aluminum trichloride in nitrobenzene solution to give 2-(2-hydroxyphenyl)- and 2-(4-hydroxyphenyl)benzimidazoles, but no photo-Fries products.[‌487‌]

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