Crystal-to-Crystal Solid-State Photochemistry: Absolute Asymmetric β-Thiolactam Synthesis from an Achiral α,β-Unsaturated Thioamide

摘要

Absolute asymmetric induction studies in the crystalline state are of wide interest since they occur spontaneously in the absence of any outside chiral influence and are relevant to theories concerning the prebiotic origin of natural chirality. The development of photochemical reactions using chiral crystals has potential for the synthesis of optically active compounds that are difficult to prepare in other ways from the viewpoint of chemo-, regio-, and enantioseleetivity. In most cases, solid-statephotochemical reactions involve transformation of achiral molecules into racemic products because of the absence of a chiral environment for reaction through crystallization in a racemic space group. For the special cases of aehiral molecules which couldadopt a chiral conformation in the crystal lattice, the molecular environment may be chiral and present an opportunity for the induction of asymmetry into photoproducts, and several successful "absolute" asymmetric syntheses involving uriimolecular reaction have been reported. Here we report a striking example of an absolute β-thiolactam synthesis through a solid-state unimolecular photochemical reaction of achiral N,N-dibenzyl-1-cyclohexenecarbothioarnide 1 which occurs in a crystal-to-crystal manner.