Selective Intramolecular Palladium(II)-Catalyzed Aminooxygenation vs. Diamination of Alkenylureas: Efficient Microwave-Assisted Reactions to Bicyclic Piperazinones

摘要

Alkenylureas arising from glycine allyl-amides 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 σ-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 chloromethylpiperazi-none. Indeed, this latter species was isolated and proved to be capable of conversion solely into the imidazopiperazinone.