Flavonoid synthesis based on photolysis of flavan-3-ols, 3-hydroxyflavanones, and 2-benzylbenzofuranones
Irradiation of flavan-3-ols, 3-hydroxyflavanones, and 2-benzylbenzofuranones in methanol leads mainly to photochemical opening of the heterocyclic ring, or to its complete photofragmentation, the products being trapped by reaction with the solvent. Fission of exocyclic C–O bonds also occurs, accompanied by intramolecular rearrangements. The course of these reactions is often dependent on the position and nature of substituents.
The conversions provide novel routes to 1,3-diaryl-1-methoxypropan-2-ols, 1,3-diaryl-2,2-dimethoxypropan-1 -ones, cis-3-methoxyflavanones, isoflavones, flavanones, and trans-chalcones, and hence to α-hydroxychalcones, cis- and trans-α-methoxychalcones, and 2-methoxy-2-(α-methoxybenzyl)benzofuranones.