Competitive cyclisations of singlet and triplet nitrenes. Part 9. 2-(2-Nitrenophenyl)-benzothiazoles and -benzimidazoles
Abstract
2-(2-Nitrophenyl)benzothiazole, produced by deoxygenation of the corresponding nitro-compound or by thermolysis or photolysis of the related azide, gives indazolo[3,2-b]benzothiazole by attack on the benzothiazole nitrogen. Similar attack of the nitrene in 2-(2-nitrophenyl)benzimidazoles gives benzimidazoindazoles in good yield. However, with an appropriate 1-substituent in the benzimidazole (e.g. Me or CHMe2) the nitrene in its triplet state (generated by acetophenone-sensitised photolysis or by thermolysis of the azide bearing a 4-dimethylamino-group) preferentially attacks this substituent giving benzimidazoquinazolines.