A Palladium Iodide-Catalyzed Oxidative Aminocarbonylation-Heterocyclization Approach to Functionalized Benzimidazoimidazoles

A novel carbonylative approach to the synthesis of functionalized 1H-benzo[d]imidazo[1,2-a]imidazoles is presented. The method consists of the oxidative aminocarbonylation of N-substituted-1-(prop-2-yn-1-yl)-1H-benzo[d]imidazol-2-amines, carried out in the presence of secondary nucleophilic amines, to give the corresponding alkynylamide intermediates, followed by in situ conjugated addition and double-bond isomerization, to give 2-(1-alkyl-1H-benzo[d]imidazo[1,2-a]imidazol-2-yl)acetamides. Products were obtained in good to excellent yields (64-96%) and high turnover numbers (192-288 mol of product per mol of catalyst) under relatively mild conditions (100 °C under 20 atm of a 4:1 mixture of CO-air), using a simple catalytic system, consisting of PdI2 (0.33 mol %) in conjunction with KI (0.33 equiv).