Abstract:

Oxidation of αtetralone ethoxycarbonylhydrazone(1) with lead tetraacetate afforded the bicyclic geminal ethyl azoester 2. On addition of equimolecular aluminum trichloride, the azocarbenium salt 3 was generated in situ as a reactive intermediate, which could be trapped by the cycloadditions to the triple bonds of nitriles giving 3H1,2,4-triazolium salts. These initially cycloadducts couldn′t be isolated but underwent smooth 1,2-aryl-shift with concurrent ring enlargement and insertion of a nitrogen atom to the carbon skeleton to provide the tricyclic salts 4a—4c, from which the literature unprecedentate ［1,2,4］triazolo［1,5-a］［1］benzazepinium picrates 6a—6c were obtained in 23%~56% yields upon hydrolytic removal of the Nethoxycarbonyl group and subsequent treatment of the resulted heterocycles 5 with picric acid. Analogously, the novel 4,5dihydro-［1,2,4］triazolo［1,5-a］quinolinium picrates(12a—12c) were prepared from 2,3dihydro-1-indanone in moderate yields.

Key words: 1,3-Dipolar cycloaddition; Ring enlargement; ［1,2,4］Triazolo［1,5a］［1］benzazepine; ［1,2,4］Triazolo［1,5-a］quinoline