Photoinduced Reductive [4 + 2] Cycloaddition of Nitroarenes

Direct C-N bond formation from nitroarenes is a valuable synthetic tool for quick access to aniline derivatives. Transformation via nitroso intermediates could be useful due to their unique properties, but the generation of nitrosoarenes in situ from nitroarenes is challenging due to the tendency for various side reactions. Herein we report the photoinduced reductive [4 + 2] cycloaddition of nitroarenes. The method begins with the photoinduced reduction of nitroarenes to give nitrosoarenes by hydrogen atom abstraction (HAA). The generated nitrosoarenes undergo a nitroso Diels-Alder (NDA) reaction. The key to success is the use of N-heterocyclic carbene (NHC) borane, which promotes efficient HAA, enabling the NDA reaction to proceed without the need for transition metals, strong bases, or elevated temperatures. The developed conditions allow high functional group tolerance, enabling late-stage functionalization and further derivatization of biologically active compounds.