Photocyclization of 2'-Hydroxychalcones to 4-Flavanones

Article abstract of DOI:10.1246/bcsj.53.518

On irradiation with light of λ<*>365 nm, parent and methoxy-substituted 2'-hydroxychalcones undergo facile photocyclization to give corresponding 4-flavanones in high efficiencies in ethyl acetate or dioxane, whereas in low or nil efficiencies in benzene, chloroform, carbon tetrachloride, ether, acetonitrile, ethanol, or t-butyl alcohol.The low reactivity in benzene is, however, significantly increased by the addition of liquid paraffin to increase the solent viscosity. 3',4'-Benzo-2'-hydroxychalcone showed low reactivities in any solvents.The formation of 4-flavanones is neither quenched by triplet quenchers nor depressed by the addition of free radical scavengers.The reaction mechanism is discussed in terms of enolization.