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

5. Alkenylureas I (R = c-C6H11, PhCH2; R' = Ph, 4-ClC6H4, 4-NO2C6H4, 2-NO2C6H4, 4-MeOC6H4) arising from glycine allylamides, were shown to be suitable substrates for the synthesis of bicyclic five-membered ring-fused piperazinones. The reported intramol. domino processes, performed under oxidative conditions with bis(acetonitrile)palladium dichloride as catalyst and copper(II) chloride in a stoichiometric amt. by microwave activation, were completely selective, involving either diamination, i.e. II, or aminooxygenation, i.e. III. While the latter process is detd. 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 (chloromethyl)piperazinone. Indeed, this latter species was isolated and proved to be capable of conversion solely into the imidazopiperazinone.