Photochemical Transformations and Laser Flash Photolysis Studies of 1,4- and 1,2-Epoxy Compounds Containing 1,2-Dibenzoylalkene Moieties

Article abstract of DOI:10.1021/jo00196a013

Photochemical transformations of a few 1,4- and 1,2-epoxy ketones have been investigated.Irradiation of a benzene solution of 1 gave a mixture of 3 (32percent) and dibenzoylacetylene (DBA, 6, 13percent), whereas the photolysis of 8 in methanol gave a mixture of the ester 12 (56percent) and DBA (22percent).Irradiation of 14 in benzene gave a mixture of the isomeric lactone 17 (25percent), 1,3-diphenylisobenzofuran (20, 20percent), and o-dibenzoylbenzene (23, 10percent).The photolysis of 24 in both benzene and methanol resulted in isomerization to the anthracene derivative 25 (6percent and 20percent).The same product (25, 38percent) was obtained in the thermolysis of 24.Plausible mechanisms for the formation of the various products have been discussed.Laser flash photolysis (337.1 nm) of 1, 8, and 14 in benzene and methanol led to the observation of short-lived transient species, characterized by absorption maxima at 405-490 nm and by lifetimes (τ_T) in the range 0.4-2.0 μs.Pulse-radiolytic observation of the same transients under energy-transfer sensitization as well as detailed quenching studies using oxygen, di-tert-butylnitroxide, azulene, ferrocene, and β-carotene led to the assignments of the transients as triplets.The quantum yields of triplet formation (Φ_T) under direct laser excitation were estimated to be high (0.50-0.74).Upon laser flash photolysis, 24 produced the anthracene derivative 25 nearly within the laser pulse; the intermediacy of a triplet with τ_T ca.7 ns and Φ_T ca.1 was established in this case by quenching studies involving 1-methylnaphthalene and 2,5-dimethyl-2,4-hexadiene.