1967 Volume 40 Issue 9 Pages 2129-2134
Photoreactions of conjugated or non-conjugated, five-membered, cyclic ketones were investigated. Irradiation of 2,3,4,5-tetraphenyl-2-cyclopenten-1-one in 2-propanol with ultraviolet light under a slow stream of nitrogen or oxygen gave 1-oxo-2,3-diphenyl-2,3-dihydro-1H-cyclopenta[l]phenanthrene (55%) and 1-oxo-3-hydroxy-2,3-diphenyl-2,3-dihydro-1H-cyclopenta[l]phenanthrene (about 20%). Similar irradiation of 3,4-diphenyl-3-cyclopenten-1-one under a nitrogen stream gave 2-oxo- and 2-hydroxy-2,3-dihydro-1H-cyclopenta[l]phenanthrene in 33% and 11% yields respectively. In both cases, there was observed photocyclization of a cis-stilbene skeleton to a phenanthrene. However, on irradiation of 2,2-dimethyl-3,4-diphenyl-3-cyclopenten-1-one, there was obtained a decarbonylation product, 1,1-dimethyl-1,2-dihydrocyclobuta[l] phenanthrene. The reaction courses of these photoreactions are proposed.
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