title: Absolute asymmetric photocyclization of isopropylbenzophenone derivatives using a cocrystal approach involving single-crystal-to-single-crystal transformation.
abstract: Absolute asymmetric photocyclization of isopropylbenzophenone derivatives was achieved by means of a cocrystal approach. Three chiral salt crystals formed by carboxylic acid derivatives with achiral amines could be prepared by spontaneous crystallization. In the M-crystal of 4-(2,5-diisopropylbenzoyl)benzoic acid with 2,4-dichlorobenzylamine, a twofold helical arrangement occurs in a counterclockwise direction to generate the crystal chirality. Conversely, the clockwise helix exists alone in the P-crystal. Irradiation of the M-crystal at >290 nm caused highly enantioselective Norrish type II cyclization to give the (R,R)-cyclopentenol, (R)-cyclobutenol, and (R)-hydrol in a 6:3:1 molar ratio, resulting in successful absolute asymmetric synthesis, while irradiation at around 350 nm afforded the (R,R)-cyclopentenol as the sole product. The reaction proceeded via single-crystal-to-single-crystal transformation, and therefore the reaction path producing the (R,R)-cyclopentenol could be traced by X-ray crystallographic analysis before and after irradiation.
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Ehime University, Matsuyama 790-8577, Japan. koshima@eng.ehime-u.ac.jp
authors.forename: Hideko
authors.initials: H
authors.lastname: Koshima
authors.forename: Hirohisa
authors.initials: H
authors.lastname: Kawanishi
authors.forename: Masaki
authors.initials: M
authors.lastname: Nagano
authors.forename: Haitao
authors.initials: H
authors.lastname: Yu
authors.forename: Motoo
authors.initials: M
authors.lastname: Shiro
authors.forename: Takaaki
authors.initials: T
authors.lastname: Hosoya
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Uekusa
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ohashi