Divergent Multicomponent Tandem Palladium-Catalyzed Aminocarbonylation-Cyclization Approaches to Functionalized Imidazothiazinones and Imidazothiazoles

The reactivity of 2-(prop-2-ynylthio)imidazoles under PdI2/KI-catalyzed oxidative aminocarbonylation conditions has been studied. Under relatively mild conditions [0.33-1 mol % of catalyst at 100 °C in MeCN and under 20 atm (at 25 °C) of a 4:1 mixture of CO-air] and in the presence of an equimolar amount of a secondary nucleophilic amine, substrates unsubstituted or bearing a single substituent on the imidazole ring were directly converted in a multicomponent fashion into functionalized imidazothiazinones. This transformation occurred through a novel auto-tandem catalysis process involving two concatenated catalytic cycles, both catalyzed by PdI2: oxidative aminocarbonylation of the terminal triple bond / cyclocarbonylation. On the other hand, 4,5-disubstituted substrates, in the presence of an excess of secondary amine, selectively led to functionalized imidazothiazoles, through an oxidative aminocarbonylation / conjugate addition process.