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Issue 3, 2000
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Effects of methylene chains on photoreactions of diphenylalkanediones and phenylalkenones

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Upon conventional UV-irradiation of 1,ω-diphenylalkane-1,ω-dione (PhC(O)–(CH2)n–C(O)Ph, n = 5, 6, 7, 8, and 10) in acetonitrile using a medium-pressure Hg lamp, an intramolecular γ-hydrogen abstraction of the triplet ketone (type II photoreaction) occurred to give acetophenone and 1-phenylalk-n-en-1-one (PhC(O)–(CH2)n − 3–CH[double bond, length half m-dash]CH2), respectively, in a 1∶1 product ratio. Type II photoreaction occurred in all the 1,ω-diphenylalkane-1,ω-diones. The product 1-phenylalk-n-en-1-one also underwent a photoreaction to give secondary products under prolonged photoirradiation. The secondary products obtained from 1-phenylalk-n-en-1-one varied with the number of the methylene group n. For instance, no reaction occurred on the photolysis of 1-phenylbut-4-en-1-one obtained from type II photoreaction of 1,7-diphenylheptane-1,7-dione (n = 5). On the other hand, 1-phenylhex-5-en-1-one from the photoreaction of 1,8-diphenyloctane-1,8-dione (n = 6) gave acetophenone, buta-1,3-diene, 1-phenylhex-4-en-1-one, 2-vinyl-1-phenylcyclobutan-1-ol, and 1-phenylcyclohex-3-en-1-ol. Photolyses of other 1,ω-diphenylalkane-1,ω-dione (n = 7, 8, and 10) gave similar secondary products. Consequently, type II photoreaction of 1,ω-diphenylalkane-1,ω-dione occurs in which the number of methylenes between the two benzoyl groups does not affect the products. On the other hand, the length of the methylene group influences the photoreaction of 1-phenylalk-n-en-1-ones.

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Article information

16 Aug 1999
11 Nov 1999
First published
25 Jan 2000

J. Chem. Soc., Perkin Trans. 1, 2000, 415-420
Article type

Effects of methylene chains on photoreactions of diphenylalkanediones and phenylalkenones

M. Nakamura, M. Miki and T. Majima, J. Chem. Soc., Perkin Trans. 1, 2000, 415
DOI: 10.1039/A906631D

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