Palladium-catalyzed intramolecular reactions of indolyl allenamides

The allene derivatives and allenamides in particular represent a versatile class of building blocks for generating nitrogen-containing heterocycles.1 The present work is regarding the behavior of allenamides derived from indole-2-carboxylic acid. The cyclization reactions occurred following different pathways but in all cases involving the carbon in the -position of the 1,2-diene. The carbopalladation of the allene moiety, through the formation of a -allylpalladium intermediate, resulted in the carboamination process in the presence of aryl iodides. By using a substituted o-arylhalide allenamide as substrate a double intramolecular version of the process was observed with the formation of a new pentacyclic fused-rings system. The carboamination step was performed also under carbonylative conditions providing the imidazo[1,5-a]indole derivative bearing an enone moiety. An unusual different outcome was observed when working in the absence of the aryl iodide. This activation led to an interesting hydroamination process, rarely reported in the presence of palladium complexes.2 This reaction proceeded exclusively under microwave irradiation.