Synthesis of five-membered nitrogen heterocycles from iron-substituted enals: Novel insight into the eta(5)-cyclopentadienyl(dicarbonyl)iron residue as a versatile functional group

Dihydropyrrolones have been synthesized from beta-cyclopentadienyl(dicarbon yl)iron-substituted enals and primary amines in a novel titanium-mediated i ntramolecular reaction cascade. The iron compounds were readily prepared fr om the corresponding beta-halogeno-substituted enals, Experimental studies, carried out to provide mechanistic details, support the key role of the ti tanium hemiaminal functionality in the reaction cascade and are in agreemen t with a carbonylation-reductive elimination sequence prior to the reductio n of the hemiaminal, which involves a pi-alkene-hydridoiron intermediate.