A bio-inspired synthesis of hybrid flavonoids from 2-hydroxychalcone driven by visible light

A bio-inspired synthesis of hybrid flavonoids from 2-hydroxylchalcone is described. Under the irradiation of 24 W CFL, 2-hydroxychalcone reacts with various nucleophiles to deliver structurally diverse hybrid flavonoids in good to excellent yields in the presence of a catalytic Brønsted acid. Moreover, moderate enantioselectivities could be obtained using a catalytic chiral phosphoric acid via counter anion directed addition. Based on mechanistic studies, the reaction is proposed to proceed via tandem double-bond isomerization/dehydrated cyclization of 2-hydroxychalcone to form a transient flavylium cation, which is in situ captured by nucleophiles to afford hybrid flavonoids. An efficient protocol for the synthesis of hybrid flavonoids was achieved via a bio-inspired tandem reaction of 2-hydroxychalcone with various nucleophiles.