Palladium(II)/copper halide/solvent combination for selective intramolecular domino reactions of indole carboxylic acid allylamides. An unprecedented arylation/esterification sequence

Abstract

Intramolecular oxidative palladium-catalyzed reactions of indolylallylamides in the presence of the couple bis(acetonitrile) palladium dichloride and copper(II) halide are described. Starting from 2- and 3-indolylallylamides and involving in both cases the C-3 position of the indole nucleus, variously substituted beta-carbolinones were obtained by arylation/halogenation, arylation/esterification or arylation/carboalkoxylation processes. On the other hand, an unusual aminohalogenation/halogenation sequence performed on 2-indolylallylamides gave rise to pyrazino[1,2-a]indole products. The carboesterification process is the result of an unknown path that involves the DMF or DMA used as solvent. The outcome of the reactions of the 3-indolylallylamides arises from a totally selective 1,2-migration of the acyl group on the supposed spiro intermediates formed from the nucleophilic attack of the C-3 indole position