Selective intramolecular palladium(II)-catalyzed aminooxygenation vs. diamination of alkenylureas: efficient microwave-assisted reactions to bicyclic piperazinones

Alkenylureas arising from glycine allylamides were proven to be suitable substrates for the synthesis of bicyclic five-membered ring-fused piperazinones. The reported intramolecular domino processes, performed under oxidative conditions with bis(acetonitrile)palladium dichloride as catalyst and copper(II) chloride in a stoichiometric amount by microwave activation, were completely selective, involving either diamination or aminooxygenation. While the latter process is determined by the direct intervention of the urea oxygen on the sigma-alkylpalladium intermediate, the diamination reaction can in principle derive from a direct attack of the second nitrogen atom on the palladium complex or on the first formed chloromethylpiperazinone. Indeed, this latter species was isolated and proved to be capable of conversion solely into the imidazopiperazinone.