Reactivity of Nitroarenes toward Alkyl Radicals Enables Direct C–H Alkylation

Abstract

Friedel–Crafts alkylation is a cornerstone transformation for arene functionalization; however, strongly electron-deficient nitroarenes fail to undergo alkylation under conventional conditions. This long-standing limitation is notable given the prevalence of nitroarenes in pharmaceuticals and agrochemicals and their central role as synthetic building blocks. Here we report a photocatalytic strategy that overcomes this challenge, enabling direct C–H alkylation of nitroarenes using readily available carboxylic acids as alkyl radical precursors. Under mild conditions, alkyl radicals generated through a decarboxylative process add preferentially to the aromatic π-system while preserving the nitro functionality, suppressing competing oxygen-atom transfer and reduction pathways. This transformation is compatible with a wide range of nitroarenes and carboxylic acids and tolerates diverse functional groups. Mechanistic studies support a pathway involving decarboxylative radical addition, followed by oxidation and rearomatization mediated by an organophotocatalyst. The photocatalytic strategy is also applicable to alkyltrifluoroborates as alternative alkyl radical precursors. This method enables late-stage functionalization of complex nitroarenes and bioactive molecules, providing a modular platform for sequential C–H diversification and expanding the synthetic utility of nitroarenes.