Intramolecular nucleophilic carbonyl trapping of alpha-ketenyl radicals by an amino group

Free-radical carbonylation of omega-alkynylamines with tributyltin hydride gives a mixture of alpha-methylene lactams and alpha-stannylmethylene lactams. Nucleophilic addition of an internal amino group to the carbonyl group of alpha-ketenyl radicals is proposed as the cyclization step. The subsequent unusual 1,4-H shift from the resulting 1-hydroxyallyl radical, followed by elimination of the beta-tributyltin radical leads to the formation of alpha-methylene lactams.