Theoretical Investigation on Iodine-Catalyzed Aerobic Oxidation of 2-Picolyl Ketone With 1,2-Diaminobenzene in Synthesis of Quinoxaline

The first theoretical investigation was provided by our DFT calculation on I2-catalyzed aerobic oxidation of 2-picolyl ketone leading to 1,2-dicarbonyl compound with 1,2-diaminobenzene. Initially, the 2-picolyl ketone is coordinated with molecular iodine to realize iodination. Promoted by base, one hydrogen iodide is assembled and cleaved producing an N-iodo species. Then, the homolytic cleavage of N−I bond gives C-centered radical, which is bonded with additional molecular oxygen forming peroxide radical. Subsequently, a second C-centered radical couples with peroxide radical yielding peroxide dimer, which undergoes homolytic O−O bond cleavage giving two oxy-radical. After removal of second hydrogen iodide, the reaction of iodine radical I• with oxy-radical forms 1,2-dicarbonyl compound. Via three steps of condensation between 1,2-diaminobenzene and 1,2-dicarbonyl compound, the product quinoxaline is finally yielded. The condensation in last step is rate-limiting for I2 -catalyzed aerobic oxidation of 2-picolyl ketone with 1,2-diaminobenzene to quinoxaline