Kenichi Nakabayashi

Efficient cross-photocycloadditions of 3-vinylcoumarins to olefins

Efficient cross-photoaddition of 3-(trans-1-propenyl)coumarin (1a) to olefins occurred to give the corresponding 4 and/or 5-substituted 3-(trans-1-propenyl)-3,6-dihydrocyclobut[c]-2-coumarin (3) in relatively good yields without the formation of dimer of 1a.

Mechanistic studies for cross-photocycloadditions of 3-vinylcoumarin derivatives to electron-rich olefins

Abstract Efficient cross-photoaddition of 3-( trans -1-propenyl)coumarin ( 1a ) to olefins occurred to give the corresponding 4- and/or 5-substituted 3-( trans -1-propenyl)-3,6-dihydrocyclobut[ c ]-2-coumarin in relatively good yields without the formation of dimer of 1a . The photoaddition of 3-ethenylcoumarin ( 1b ) and 2-ethenyl-8-methoxycoumarin ( 1c ) to 2,3-dimethyl-2-butene ( 2a ) gave the corresponding cycloadducts along with the formation of the photodimers of 1b or 1c . Kinetic data show that the photoaddition of 1a to 2a in benzene proceeds via a singlet exciplex between 1a and 2a and the photoaddition in acetonitrile proceeds via a termolecular interaction of a polar exciplex with another 2a .

Valence isomerization of quadricyclane-norbornadiene derivatives via triplet state. Correlation of the mechanism with triplet conformation of the olefinic moiety

The mechanism of the valence isomerization between methyl 5-aryl-tetracyclo[3.2.0.02,704,6]-heptane-1-carboxylate (1) and methyl 3-aryl-bicyclo[2.2.1]hepta-2,5-diene-2-carboxylate (2) under the triplet sensitization in benzene has been studied by pulse radiolysis and stationary experiments. The valence isomerization proceeds via a 1,3-biradical intermediate favorably to 1 for the phenyl derivatives where the most stable conformation of the corresponding olefinic analogue is a twisted form. In the case of 1-naphthyl derivatives where the conformation of the olefinic analogue is a planar form, an adiabatic cycloreversion of 1 to 2 takes place. An equilibrium state between a 1,3-biradical intermediate and a triplet state with a structure of norbornadiene is estimated for 2-naphthyl derivatives. Correlation of the mechanism for the valence isomerization with the conformation of corresponding olefinic analogue has been discussed on the basis of the potential energy surfaces for the isomerization.