Nucleophilic attack on 4,7-disubstituted benzofurazans and their N-oxides: synthesis of tetrazolo[1,5-a]azepines

Abstract

The reaction of various nucleophiles with benzofurazans and their N-oxides carrying electron-attracting substituents in the 4 and 7 positions has been reviewed and the study extended to include sulphonyl groups. As well as the simple replacement of leaving groups typical in chloronitrobenzofurazans, some unusual reactions were observed. Secondary amines attacked the heterocyclic N of benzofurazan N-oxide bis(methylsulphones) to give arylhydrazines, and this pathway was also followed to some extent in the reaction of the weaker base morpholine with bis(arylsulphones). Sodium azide reacted with benzofurazan N-oxide bis-sulphones to yield tetrazolo[1,5-a]azepines, possibly by a mechanism involving attack at the bridgehead carbon. Syntheses of tetrazoles are briefly reviewed with regard to mode of ring closure. Nitrobenzofurazan N-oxide sulphones yielded both azidosulphones and tetrazolo[1,5-a]azepines. The N→S migration of oxygen noted for nitrobenzofurazan N-oxide sulphoxides was also observed for sulphone sulphoxides.