Formation of Amidinyl Radicals via Visible-Light-Promoted Reduction of N-Phenyl Amidoxime Esters and Application to the Synthesis of 2-Substituted Benzimidazoles.

We have developed a new method for the synthesis of 2-substituted benzimidazoles via amidinyl radicals generated by visible-light-promoted reduction of N-phenyl amidoxime esters in the presence of an iridium photocatalyst. This is the first report of the use of N-phenyl amidoxime esters as amidinyl radical precursors, and the first use of substituted benzene rings as amidinyl radical acceptors. This method widens the application range of substrates and overcomes the shortcomings of the traditional methods for the synthesis of 2-substituted benzimidazoles, which requires harsh reaction conditions, involves difficult-to-prepare substituted o-phenylenediamine substrates, and produces acidic waste.