Intramolecular addition of acyldiazenecarboxylates onto double bonds in the synthesis of heterocycles
作者:José V. Prata、Dina-Telma S. Clemente、Sundaresan Prabhakar、Ana M. Lobo、Isabel Mourato (in part)、Paula S. Branco (in part)
DOI:10.1039/b110414d
日期:2002.2.6
Appropriate aryl-substituted unsymmetrical azodicarbonyl compounds, generated from bishydrazides by oxidation, undergo intramolecular cyclisations to furnish a variety of useful heterocycles such as N-substituted oxindoles, carbostyrils, benzazepinones, benzazocinones, benzimidazolones, benzoxazinones and pyrazolones in varying degrees of efficiency. Methods are described to remove the N-acyl groups from the heteroaromatic compounds. Under mildly acidic conditions where equal opportunities are available for an ipso or a normal cyclisation it is the former process that occurs preferentially. Evidence is presented in favour of a C-to-C migration in the ipso product for the formation of a methoxy-substituted carbostyril derivative. One of the spiro substances is shown to participate in dienone–phenol rearrangement to provide the corresponding quinolone–phenol in high yield.