Tungstate-Catalyzed Bioinspired Decarboxylative Halogenation of Electron-Deficient (Hetero)Phenolic Acids

Abstract

Phenolic acids (PAs) can be derived from lignin, and their value-added transformations provide a good renewable source for arenes. The halogenase-catalyzed decarboxylative halogenation of PAs is a key step in the biosynthesis of many halogenated natural products. Inspired by halogenase, herein we present a synthetically useful tungstate-catalyzed decarboxylative halogenation of electron-deficient (hetero)phenolic acids under mild conditions, based on which the antibiotic bromophene and its analogues were prepared concisely. Mechanism studies support the halogenation−decarboxylation procedure, but the decarboxylation−halogenation pathway cannot be excluded. Additionally, the chloride can reverse the selectivity between bromination and iodination in this reaction, somehow providing a useful perspective for the halide selectivity in vanadiumdependent haloperoxidase in seawater.

One-pot ipso-hydroxylation and ortho-/para-halogenation of (hetero)arylboronic acids under tungsten catalysis

“…15 One of the basic mechanisms of H 2 O 2 oxidation is non-radical (ionic) hydroxyl transfer, in which the HO-OH bond is polarized for nucleophilic substitution. Based on our recent research on tungsten-catalyzed halogenations 16 inspired by the function of vanadium-dependent haloperoxidase (VHPO), 17 the tungstate ( W-I ) could activate the HO–OH bond by forming a W-η 2 -peroxox intermediate ( W-II ), which then could be cleaved by halide. This process could be assisted by a Brønsted or Lewis acid, ultimately affording the hypohalite, which could then be trapped by arenes (Scheme 1A).…”

Sodium Tungstate Dihydrate (Na2WO4·2H2O): A Mild Oxidizing and Efficient Reagent in Organic Synthesis

“…J) Ma and Chen published the tungstate-catalyzed decarboxylative bromination of 3-hydroxy-2-methylquinoline-4-carboxylic acid to furnish 4-bromo-2methylquinolin-3-ol 15. …”