X-Ray crystallographic analysis and photochemical reaction of asymmetrically substituted alpha,beta-unsaturated thioamides

摘要

Photochemical reaction of asymmetrically substituted N-benzyl-N-isopropyl-alpha,beta-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 H-1 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 beta-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 beta-thiolactam product. [References: 17]