Photoinduced Electron Transfer Reaction of Pyrazoline Derivatives. Formation of Rearrangement Product

• Published in: Journal of organic chemistry Vol. 60; no. 25; pp. 8270 - 8277
• Main Authors: Karatsu, Takashi, Itoh, Hiroki, Kikunaga, Toshiyuki, Ebashi, Yoshinori, Hotta, Hiroko, Kitamura, Akihide
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 01.12.1995; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; 1-PYRAZOLINES; 2,3-DIAZABICYCLO<2.2.2>OCT-2-ENES; OXYGENATION; RADICAL CATIONS; DECOMPOSITION; PHOTOCHEMISTRY; BICYCLIC AZOALKANES; AZO-COMPOUNDS; PHOTOELECTRON-SPECTROSCOPY; ATOM TRANSFER
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo00130a030

The initial process of photoinduced electron transfer (PET) between electron deficient sensitizers and r-3-(methoxycarbonyl)-t-4-(para-substituted-phenyl)-3,5,5-trimethyl-1-pyrazolines 1 was investigated. Fluorescence quenching rate constants of the sensitizers by 1 and PET decomposition quantum yields of 1 reflect that the stability of the generated radical cations of 1 and the back-electron transfer play important roles in the reactivity. The generated radical cations of 1 followed by nitrogen elimination gave cyclopropane derivatives 2 and/or aryl migrated olefins 3. Product distributions between the cyclopropanes 2 and the olefins 3 depend on the para-substituent of the phenyl ring of 1. Semiempirical MO calculations (AM1) of the radical cations of 1 suggest the location of the spin and the charge governing the product distribution.