Palladium(II)-catalyzed cyclization of heterocyclic ketene aminals with (E)-ethyl 2,3-diiodoacrylates: selective synthesis of bicyclic pyrroles and bicyclic pyridones

A concise and efficient synthesis of novel bicyclic pyrroles has been achieved by PdCl₂-catalyzed cyclic condensation of six-membered heterocyclic ketene aminals (HKAs) or seven-membered HKAs with ethyl 2,3-diiodoacrylate and diethyl 2,3-diiodofumarate in the presence of Cs₂CO₃, respectively. A series of novel bicyclic pyridones have also been obtained via five-membered HKAs with diethyl 2,3-diiodofumarate under the optimized conditions in moderate yields. These reactions are the first application of a transition metal to catalyze the building blocks HKAs to form the bicyclic pyrrole library via condensation reaction.