Irradiation of benzotriazoles 1a-e at λ = 254 nm in acetonitrile solution generated the corresponding 1,3-diradicals which underwent intermolecular cycloaddition with maleimides to afford the corresponding dihydropyrrolo [3,4-b]indoles and with acetylene derivatives to afford indoles as the major products. This offers an interesting and simple access to such ring systems of potential synthetic and biological interest. The structures of the photoproducts were established spectroscopically and by single crystal X-ray crystallography.

Abstract:Irradiation of an acetonitrile solution of 4-aryl-3,5-dibenzoyl-1,4-dihydropyridine derivatives 1a-c and maleimides 2a-c using medium pressure Hg-arc lamp (λ > 290) nm afforded three different cycloadducts 4, 5, 6 in addition to the oxidation products 3. These results indicate that compounds 1a-c undergoes intermolecular cycloaddition reaction through three biradical intermediates and behave photochemically different than those reported previously for the analogous 3,5-diacetyl and 3,5-dicarboxylic acid derivatives. The present work also offers simple access to novel tricyclic and tetracyclic nitrogen heterocyclic ring systems of potential biological and synthetic applications. The structure of the photoproducts was established spectroscopically and by single crystal X-ray crystallography.

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Abstract. Methyl-, ethoxy-, and phenyl-substituted acrylonitriles undergo efficient 1,2-photocycIoaddition to 4-cyanoanisole, but the azocine formation of the parent addend is inhibited by these groups. The regiochemistry, selectivity and efficiency of the cycloaddition of acrylonitrile to cyanomethoxyanisoles vary markedly with the position of the arene substituents and reflect competition between the influences of the cyanoanisole and dimethoxybenzene moieties. Chemical-Abstract names4-cyanoanisole = 4-methoxybenzonitrile 2-methoxy-4-cyanoanisole = 3,4-dimethoxybenzonitrile anisole = methoxybenzene acrylonitrile = 2-propenenitrile methacrylonitrile = 2-methyl-2-propenenitrile 4-cyanoanisole = 4-methoxybenzonitrile cinnamonitrile = 3-phenyl-2-propenenitrile maleimide = 'H-pyrrole-2,5-dione 4-cyanocinnamonitrile = 4-(2-~yanoethenyI)benzonitrile the ortho photocycloaddition of acrylonitrile to benzenes which have an electron acceptor and an electron donor group in the 1,4 positions, is accompanied by substantial amounts of azocines formed by photoaddition of the addend nitrile to the arene"'. For photoreactions to be widely adopted as synthetic procedures, the basic process must not be adversely affected by reactant substituents. Thus, in order to assess the scope of the above addition processes and the ability of reactant substituents to direct the mode and positions of addend attack on the arene, we have studied the photoreactions of several acrylonitrile derivatives with 4-cyanoanisole and of acrylonitrile with various substituted anisoles.

Irradiation of 1-substituted benzotriazole arylhydrazones 3a–c, 4a,b and 5a,b with a 16 W low pressure mercury arc-lamp (254 nm) for 24 h gave phenanthridin-6-yl-2-phenyldiazines 9a–c, phenanthridin-6(5H)-ones 10a–c, 1-anilinobenzimidazoles 11a–c, 2-aryl-1H-benzimidazoles 12a–c, 1-arylamino-1H-benzimidazol-2-carboxylic acid ethyl esters 14a,b, 1-aryl-1H, 9H-benzo [4,5][1,2,3] triazolo[1,2-a]tetrazole-3-carboxylic acid ethyl esters 16a,b, 1-arylamino-2-benzoylbenzimidazoles 18a,b and 2-benzoylbenzoxazole 21.

Under photolysis conditions involving irradiation with a 16 W low pressure mercury arc-lamp (254 nm) or sunlight, functionally substituted 1-vinylbenzotriazoles react efficiently to produce 2-acylindoles, 2-benzotriazol-1-yl-4-methylquinolin-3-ol, isatin, indolo[2,1-b]quinazoline-6,12-dione (tryptanthrin) and dihydropyrazolo [4,3-b]indole.

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