ENANTIODIFFERENTIATING CIS-TRANS PHOTOISOMERIZATIONS OF 1,2-DIARYLCYCLOPROPANES AND 2,3-DIPHENYLOXIRANE SENSITIZED BY CHIRAL AROMATIC ESTERS

Photosensitized enantiodifferentiating cis-trans isomerizations of 1,2-diphenylcyclopropane (1), 1,2-bis(4-methoxyphenyl)cyclopropane (2), and 2,3-diphenyloxirane (3) were performed in the presence of optically active alkyl arenecarboxylates as electron-accepting photosensitizers. Several photosensitizers possessing different chromophores and chiral groups were examined in polar and nonpolar solvents, and optical purities (op) up to 10% for It and 1% for 2t and 3t were obtained. The product's op varied drastically with solvent polarity and, in an extreme case, typical polar and nonpolar solvents gave antipodal products. Mechanistic investigations revealed that the enantiodifferentiation occurs in the quenching of the excited chiral sensitizer by racemic substrates and that full equilibrium is not established between the enantiomeric ambident intermediates, probably owing to their short lifetimes.