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Communication | Regular issue | Vol 85, No. 5, 2012, pp.1053-1060
Published online, 27th March, 2012
DOI: 10.3987/COM-12-12449
Photoinduced Selective Transformation of N-Acyl-α-dehydro(9-phenanthryl)alaninamides into Their Cyclization Intermediates in a Polar Protic Solvent

Yuki Kawanishi, Hiroko Yoshiie, Tetsutaro Igarashi, and Tadamitsu Sakurai*

*Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan

Abstract

Irradiation of the title compounds [(Z)-1] in methanol afforded trans-3,8a-dihydro-2-dibenzo[f,h]quinolinone derivatives (trans-2) in preference to cis-2, all of which serve as precursors of the corresponding 3,4-dihydrodibenzoquinolinones. An analysis of the substituent and solvent effects on the cyclization occuring from the excited-state (E)-1 showed that the reactivity of this (E)-isomer is greatly influenced by the steric bulk of the alkyl group attached to the N´-amide nitrogen of the starting 1. In addition, this analysis confirmed that the stabilization of the excited-state (E)-1 (having a zwitterionic structure), by hydrogen-bonding and charge-transfer interactions with methanol, is an essential prerequisite for the occurrence of the photocyclization reaction selectively forming trans-2 and cis-2.