Photodimerization cyclopentenone

The photodimerization of 2-cyclopentenone has been studied by Eaton and Hurt<82) and Ruhlen and Leermakers<83) ... 

More recent investigations of the photodimerizations of cyclopentenone and cyclohexenone<134) have revealed that both reactions result from the lowest triplet states of the enones (Et > 70 kcal/mole), which is probably 77- 77 in character/1331 Both photodimerizations occur via reversibly... 

Nagamatsu et al. have shown that liquid crystal and various other media can greatly influence the stereochemistry of uracil photodimerization. Pirrung and Nunn have shown that irradiation of a series of quinone monoacetals (5) in acetic acid provides a flexible high-yield route to substituted cyclopentenones. 

Intermolecular photoadditions of a,/3-unsaturated carbonyl compounds can take place either at the CC or at the CO double bond. Photodimerizations with formation of a cyclobutane ring are quite common. In cases such as cyclopentenone (81), head-to-head as well as head-to-tail dimers are produced. 

The relative orientation of olefins within metal complexes provides an alternative approach to induce stereoselectivity in the cycloadditions of olefins in the solid state. Irradiation of SnCl4 complexes of cyclopentenones 14a-c in the solid state leads to stereoselective photodimerization to give a ri-HT cyclodimers 15a-c in high yields. ... 

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