title: 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.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology, NAIST, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan), Fax: (+81) 743-72-6179. ntaku@ms.naist.jp.
authors.forename: Takuya
authors.initials: T
authors.lastname: Nakashima
authors.forename: Kyohei
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kimura
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kawai
mesh_terms: D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D010777:Photochemistry; D011789:Quantum Theory; D013237:Stereoisomerism; D013455:Sulfur / Q000737:chemistry*; D013844:Thiazoles / Q000737:chemistry*
chemical_list: D013844:Thiazoles; D013455:Sulfur; D010100:Oxygen
keywords: chirality; foldamers; helical structures; photochromism; supramolecular chemistry