Facile synthesis of photoactive diaryl(hetaryl) cyclopentenes by ionic hydrogenation

A facile synthetic approach to photoactive diarylethenes comprising a cyclopentene ring as an ethene bridge was developed based on reduction of 2,3-diaryl(hetaryl)cyclopent-2-en-1-ones through an ionic hydrogenation reaction. The method provides access to unsymmetrical photoswitchable diarylethenes containing benzene, thiophene, or azoles (thiazole, oxazole, imidazole) as aromatic moieties in 40-71% yields. Diarylethenes comprising two heterocyclic moieties show typical photochromic properties, with absorption maxima of the photoinduced form in the blue region (yellow photochromes).