Chiral Photoresponsive Tetrathiazoles That Provide Snapshots of Folding States

Abstract

Herein, we designed chiral photoresponsive tetra(2-phenylthiazole)s, which induce a diastereoselective 6π-electrocyclization reaction in a helically folded structure to freeze the conformational interconversions. The folding conformation with one helical turn of tetra(2-phenylthiazole)s was supported by multiple intramolecular noncovalent interactions including vicinal S···N interheteroatom interactions and CH-π and π-π stacking interactions between nonadjacent units, as found in X-ray crystal structures as well as quantum chemical calculations. The introduction of a chiral group at both ends of tetra(2-phenylthiazole) dictates the preferential folding into a one-handed helix conformation by the simultaneous operation of S···O and multiple CH-π interactions that involve the chiral end groups. Since the tetra(2-phenylthiazole)s possess two equivalent photoreactive 6π-electron systems and the folded conformation is suitable for photoinduced electrocyclization reaction, they undergo a photocyclization reaction in a stereoselective manner to memorize the chirality of the helix in a resulting diastereomeric closed form.