Photocycloaddition reaction of tropone and electron-accepting 9,10-dicyanoanthracene

Abstract

The photoreaction of tropone 1 and electron-accepting 9,10-dicyanoanthracene (DCA) gave four products in less polar benzene while in more polar acetonitrile–dichloromethane (1∶1) solution an [8+4]π adduct was formed together with the above four products. The formation of the [8+4]π adduct was enhanced by biphenyl and quenched by 1,4-dimethoxybenzene. According to Weller’s equation, electron transfer from tropone 1 to DCA is estimated to be the endothermic (ΔG = +1.2 kcal mol^–1). The following coupling reaction between DCA^˙– and 1^˙+ to the [8+4]π adduct, however, could make the electron-transfer process shift to generate the radical-ion pair.