C–H Functionalization via Remote Hydride Elimination: Palladium Catalyzed Dehydrogenation of ortho-Acyl Phenols to Flavonoids

Although deprotonation of electron-poor C–H bonds to carbon anions with bases has long been known and widely used in organic synthesis, the hydride elimination from electron-rich C–H bonds to carbon cations or partial carbocations for the introduction of nucleophiles is a comparatively less explored area. Here we report that the carbonyl β-C(sp3)–H bond hydrogens of ortho-acyl phenols could be substituted by intramolecular phenolic hydroxyls to form O-heterocycles, followed by dehydrogenation of the O-heterocycle into flavonoids. The cascade reaction is catalyzed by Pd/C without added oxidants and sacrificing hydrogen acceptors.