Solid-State Photochemistry: Absolute Asymmetric β-Thiolactam Synthesis from Achiral N,N-Dibenzyl-α,β-unsaturated Thioamides

Several types of achiral N,N-dibenzyl-α,β-unsaturated thioamides were subjected to X-ray crystallographic analysis, and it was revealed that methylcrotonthioamide and 1-cyclohexenecarbothioamide provided chiral crystals. The absolute configuration determined by anomalous scattering method corresponded to the cotton effect in the solid-state CD spectra. The solid-state photoreaction gave optically active β-thiolactams. On the other hand, E–Z isomerization takes place in the photoreaction of a tiglylthioamide derivative. Stereochemical assignment before and after the reaction was rationalized by the hydrogen abstraction by alkenyl carbon followed by cyclization via a zwitterionic intermediate.