Photoreactions of Flavanones

Article abstract of DOI:10.1246/bcsj.53.2938

Parent and substituted flavanones undergo photochemical opening of the pyrone ring to give corresponding 2'-hydroxychalcones in benzene, acetonitrile etc., the yields varying from 0 to 70percent with substituents.The reaction is depressed by the addition of 1,3-pentadiene, nitrosobenzene, or acrylonitrile.On the other hand, flavanone and 4-chromanone undergo photoreduction in 2-propanol to give reductive coupling products and solvent adducts as isomeric mixtures. 7,8-Benzoflavanone does not undergo photoreduction in 2-propanol but the ring opening reaction instead.Mechanisms have been discussed in terms of the relative contribution of n,?^* and ?,?^* character in the lowest triplet states.