Photochemical δ-hydrogen abstraction from acyclic and semicyclic monothioimides

Abstract

Photochemical δ-hydrogen abstraction from acyclic and semicyclic monothioimides have been studied. Photolysis of acyclic monothioimides possessing a benzylic hydrogen atom at the δ-position gave γ-lactams, via a 1,5-diradical intermediate, accompanied by thioamides were generated by γ-hydrogen abstraction. Irradiation of the five-membered semicyclic monothioimide, N-(3-phenylpropionyl)pyrrolidine-2-thione, yielded 5-mercapto-4-phenyl-1-azabicyclo[3.3.0]octan-2-one. For N-(3-phenylbutyryl)pyrrolidine-2-thione, disproportionation, involving 1,6-hydrogen migration, was the main path. Photolysis of the six-membered semicyclic monothioimide, N-(3-phenylbutyryl)piperidine-2-thione, gave an unsaturated thiol, via a 1,4-hydrogen shift of a 1,5diradical intermediate, accompanied by cyclisation product and piperidine-2-thione.