Nickel-catalyzed para-selective carboxylation of phenols with CBr4/MeOH

Abstract

1,10-Phenanthroline-assisted, Ni(II)-catalyzed para-carboxylation of phenol derivatives is reported. A wide variety of substituted phenols are compatible with this reaction and led to para-carboxylated products in moderate to good yields. Impressively, various bioactive compounds are selectively carboxylated, and several bioactive molecules, including methyl syringate, methyl gallate, and dimethyl gallate, could also be directly carboxylated in one step. Mechanistic studies show that the coordination of Ni(II) with the hydroxyl group of phenol enhances the activity of hydroxyl group-bound benzene ring, leading to high para-selectivity, as influenced by the nickel catalyst and ligand steric hindrance.