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Paper | Special issue | Vol 40, No. 2, 1995, pp.597-605
Published online, 1st January, 1970
DOI: 10.3987/COM-94-S46
Synthesis of Dimethylpyrazolo[1,2-a]benzotriazoles and of Methylpyrazolo[1,2-a]quinoxalines by Cyclization of 3,5-Dimethyl-1-(2-nitrenopenyl)pyrazoles

Angelo Albini, Gianfranco Bettinetti, and Giovanna Minoli

*Dipartiment di Chimica Organica, Università di Pavia, V.le Taramelli 10, 27100 Pavia, Italy

Abstract

The thermal and photochemical decomposition of a series of 5-substituted 1-(2-azidophenyl)-3,5-dimethylpyrazoles has been examined under a homogeneous set of conditions. Cyclization to pyrazolo[1,2-a]benzotriazole (via singlet nitrene) is an efficient process except when the phenyl substituent induces intersystem crossing to the azide triplet or compensates for its electrophilicity. On the contrary, cyclization to pyrazolo[1,2-a]quinoxaline (via triplet nitrene) is not a preparatively useful process, due to competition with dimerization to the azo derivatives and reduction to aminophenylpyrazoles.