Highly Regioselective Synthesis of Multisubstituted Pyrroles via Ag-Catalyzed [4+1C]insert Cascade

An efficient [4+1C]insert approach to the coupling of enaminones with donor/acceptor or donor/donor carbenes by the AgOTf-catalyzed C–C bond carbenoid formal insertion/cyclization/[1,5]-shift cascade reaction was successfully developed, providing distinct chemo- and regioselective multisubstituted pyrroles. The plausible reaction mechanism involves two catalytic cycles: in the first one, silver ions regioselectively catalyze the C–C bond formal insertion reaction; in the second one, silver ions chemo- and regioselectively control the cyclization and [1,5]-shift reactions. This method not only provides convenience and applies atom economy in the synthesis of multisubstituted pyrroles but also presents an entry point for further pyrrole diversification via facile modification of resulting 4H-pyrrole products, as displayed by a short formal synthesis of the natural product lamellarin L.