Solid-state photochemistry of o-aroylbenzothioates:: Absolute asymmetric phthalide formation involving 1,4-aryl migration

Solid-state photoreactions of S-(o-tolyl), S-phenyl, and S-(m-tolyl) 2-benzoylbenzothioates, which formed chiral crystals by spontaneous resolution, underwent an unprecedented intramolecular cyclization involving phenyl migration to afford optically active corresponding 3-phenyl-3-(arylthio)phthalide in good chemo- and enantioselectivities. Stereochemical assignment and substituent probe experiment of this photoreaction sequence led to a reliable conclusion that this reaction was rationalized on the basis of the aryl migration rather than the well-recognized radicalic mechanism. Furthermore, the chirality preservation in the crystals was demonstrated by means of the bisignated CD spectra, which allowed assignment of the origin of the specific CD band and the helicity of the chiral molecules.