X-Ray crystallographic analysis and photochemical reaction of asymmetrically substituted α,β-unsaturated thioamides

Abstract

Photochemical reaction of asymmetrically substituted N-benzyl-N-isopropyl-α,β-unsaturated thioamides both in solution and in the solid state was investigated. All thioamides exist in an equilibrium between two rotamers owing to the rotation of the C(S)–N bond. The free energy of activation for the bond rotation was estimated by temperature-dependent ¹H NMR spectroscopy. The free energy of activation lies in a range 18.4–19.5 kcal mol^–1. Irradiation in benzene solution proceeded to give hydrogen abstraction by alkenyl carbon from both benzyl and isopropyl groups, leading to β-thiolactam and 1,3,5-dithiazinane products, respectively. Hydrogen abstraction from only the isopropyl group took place in the solid-state photolysis, giving an isomeric β-thiolactam product.