Diastereoselective cyclization in chiral diarylethene crystals: polymorphism and selectivity

structure: see text] An optically active photochromic diarylethene, (S)-1-(2-methyl-5-phenyl-3-thienyl)-2-2-methyl-5-(4-(3-methyl-1-penten-1-yl)phenyl)-3-thienyl]perfluorocyclopentene ((S)-1a), was synthesized. (S)-1a formed two crystalline phases, alpha- and beta-phases. The diarylethene underwent a photochromic reaction in solution and even in the single-crystalline phase. In solution, no diastereoselection was observed. On the other hand, in the beta-crystalline phase, only one diastereomer (S,R,R)-1b was produced. No such diastereoselection was observed in the alpha-crystalline phase.