Halogenase-Inspired Oxidative Chlorination Using Flavin Photocatalysis

Abstract

Chlorine gas or electropositive chlorine reagents are used to prepare chlorinated aromatic compounds, which are found in pharmaceuticals, agrochemicals, and polymers, and serve as synthetic precursors for metal-catalyzed cross-couplings. Nature chlorinates with chloride anions, FAD-dependent halogenases, and O2 as the oxidant. A photocatalytic oxidative chlorination is described based on the organic dye riboflavin tetraacetate mimicking the enzymatic process. The chemical process allows within the suitable arene redox potential window a broader substrate scope compared to the specific activation in the enzymatic binding pocket. Chlorination of arenes with chloride anions: The photochemical analogue of the enzymatic chlorination of Flavin-adenine dinucleotide (FAD)-dependent halogenases is possible in the presence of riboflavin, air, acetic acid, and blue light (see scheme; RFT=riboflavin tetraacetate).