Light-promoted aromatic denitrative chlorination

Abstract

Nitroarenes are readily accessible bulk chemicals and can serve as versatile starting materials for a series of synthetic reactions. However, due to the inertness of the CAr–NO2 bond, the direct denitrative substitution reaction with unactivated nitroarenes remains challenging. Chemists rely on sequential reduction and diazotization followed by the Sandmeyer reaction or the nucleophilic aromatic substitution of activated nitroarenes to realize nitro group transformations. Here we develop a general denitrative chlorination reaction under visible-light irradiation, in which the chlorine radical replaces the nitro moiety through the cleavage of the CAr–NO2 bond. This practical method works with a wide range of unactivated nitro(hetero)arenes and nitroalkenes, is not sensitive to air or moisture and can proceed smoothly on a decagram scale. This transformation differs fundamentally from previous nucleophilic aromatic substitution reactions under thermal conditions in both synthesis and mechanism. Density functional theory calculations reveal the possible pathway for the substitution reaction. Due to the inert CAr–NO2 bond, direct denitrative substitution reactions with unactivated nitroarenes are challenging. Now, using visible-light irradiation, a strategy has been developed to enable direct aromatic denitrative chlorination. Chlorine radicals can replace the NO2 moiety in a wide range of unactivated nitroarenes as well as nitroalkenes.