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8711423 
Journal Article 
Photochemical Behavior of 2-Phenylbenzoxazole. Synthesis of 1,3-Diazetidine via the Intermolecular [2π + 2π Cycloaddition of Two Carbon-Nitrogen Double Bonds 
Roussilhe, J; Fargin, E; Lopez, A; Despax, B; Paillous, N 
1983 
Yes 
Journal of Organic Chemistry
ISSN: 0022-3263
EISSN: 1520-6904 
48 
21 
3736-3741 
English 
The photochemical behavior of 2-phenylbenzoxazole (1) in cyclohexane solutions is investigated. In concentrated solutions, photodimerization of 2-phenylbenzoxazole is observed (φ ~; 0.08). In dilute solutions, this reaction is no longer efficient, and only a very slow reaction with cyclohexane takes place, leading to photoaddition and photosubstitution products with a low quantum yield (φ < 1.5 × 10~3). Photosensitization and quenching experiments as well as heavy-atom effects indicated that the two reactions derive from different excited states. The photodimerization occuss from the singlet excited state and the reaction with the solvent from the triplet state. Photodimer 2 is stable in the solid state at room temperature but reverts to 1 quantitatively in solution. The rate of the cycloreversion reaction can be enhanced either by catalysis or by irradiation. The activation barrier determined by UV measurements was found to be 90 kJ mol-1. By use of microcalorimetric experiments, the molar enthalpy of reversion was found to be -116 kJ mol-1. For application of this new system to light energy conversion, the recycling capacity of the interconvertion process as well as the heterogeneous catalysis of the thermal reversion was studied. 1983, American Chemical Society. All rights reserved.