Photochemical and Thermal Transformations of 3-Benzyl-2(3H)-furanones and Related Substrates

Article abstract of DOI:10.1021/jo00234a002

Photochemical and thermal transformations of several 2(3H)-furanones are reported.Steady-state irradiations of 3-benzyl-3,5-diphenyl-2(3H)-furanone (1a) in benzene or methanol, for example, gave a mixture of 2,3,5-triphenylfuran (3a) (8-9percent) and 1,3,5-triphenylbut-3-en-1-one (6a) (26-34percent), along with 34-37percent recovery of the unchanged starting material.Similar results were obtained with 3-benzyl-3-(4-methylphenyl)-5-phenyl-2-(3H)-furanone (1b) and 3-benzyl-3-(4-methoxyphenyl)-5-phenyl-2(3H)-furanone (1c) under analogous conditions.Upon direct irradiation, 3,3-dibenzyl-5-phenyl-2(3H)-furanone (1d), however, gave only 3-benzyl-1,4-diphenylbut-3-en-1-one (6d) (80-83percent), whereas 3-benzyl-3-phenylphenanthro<9,10-b>furan-2(3H)-one (1e) gave only 2,3-diphenylphenanthro<9,10-b>furan (3e) (15-21percent).On the other hand, 3-benzoyl-3,5-diphenyl-2(3H)-furanone (1f) gave only the bis lactone 10a (72-75percent) under direct photolysis.The bis lactones 10a-c and the rearranged 5-benzyl-3,5-diaryl-2(5H)-furanones 9a-d were the major products in the course of sensitized irradiation of 1a-d in the presence of acetophenone in benzene.The thermolysis of 1a-d also led to the formation of the rearrangement products 9a-d in high yields (60-80percent).Possible mechanisms of these various photochemical and thermal reactions are discussed in terms of singlet-mediated decarbonylation, triplet-sensitized homolysis of the benzyl-to-furanone bond and probable thermal <1,3>-sigmatropic shift of the benzyl group.The laser pulse photoexcitation (337.1 nm) of benzophenone in the presence of 1a-d in benzene of acetonitrile produces the short-lived triplets of the 2(3H)-furanones (τ_T = 0.5-3.0 μs), which subsequently undergo bond cleavage lea ding to furanoxy radicals.The spectral and kinetic features of the triplets and the radicals are presented.