Ruthenium Catalyzed One-pot Synthesis of Dihydro-pyrrol-2-one Derivatives from α,β-unsaturated Imines, Carbon Monoxide and Ethylene

The use of Ru3(CO)12 as a precatalyst induces a catalytic C–C coupling reaction of α,β-unsaturated imines with CO to yield imines with an aldehyde function in β-position with respect to the C–N double bond. An intramolecular cyclization reaction takes place via the nucleophilic attack of the imine nitrogen towards the carbonyl carbon atom building up a pyrrol-2-one system. A second ruthenium catalyzed C–C coupling reaction leads to the formal insertion of one molecule of ethylene into a C–H bond of the pyrrol-2-one in ortho position with respect to the keto group. By this selective reaction cascade imines derived from cinnamaldehyde or crotonic aldehyde, respectively, produce 1,3-dihydro-pyrrol-2-one derivatives. The analogous reaction starting from β-naphthylaldimines yields 9b-ethyl-4-propionyl-2,9b-dihydro-benzo[e]isoindol-1-one derivatives as a new class of heterocyclic compounds.