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Paper | Special issue | Vol 84, No. 2, 2012, pp.737-751
Published online, 10th August, 2011
DOI: 10.3987/COM-11-S(P)48
Enantioselective Cyclization Reactions of (Z)-N-Benzoyl-α-dehydro(1-naphthyl)alanine N’-Arylamides Initiated by Photoinduced Electron Transfer from Chiral Prolinol

Hiroyuki Yadai, Yuhki Sato, Tetsutaro Igarashi, and Tadamitsu Sakurai*

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

Abstract

An investigation was undertaken to explore substituent effects on the photoinduced electron transfer-initiated enantioselective cyclization of the title α-dehydronaphthylalanine N’-(2-hydroxyphenyl)amide [(Z)-1a], N’-(3-hydroxyphenyl)amide [(Z)-1b], N’-(4-hydroxyphenyl)amide [(Z)-1c], and N’-phenylamide [(Z)-1d] in 1,2-dichloroethane containing chiral N-methylprolinol or prolinol. 1H NMR spectral and HPLC chiral analyses of the target photoproducts, cis- and trans-4,5-dihydrooxazole isomers, confirmed that enantiomeric excess (ee) for these two isomers (estimated in the presence of the former prolinol) displayed a clear tendency to decrease in order of (Z)-1d > (Z)-1c > (Z)-1b > (Z)-1a. Hydrogen bonding and charge transfer interactions in radical ion pair and biradical intermediates were suggested to be key factors controlling ee, the value of which varied from 0 to 58%.