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Metal-Free Atom-Economical Synthesis of Tetra-Substituted Imidazoles via Flavin-Iodine Catalyzed Aerobic Cross-Dehydrogenative Coupling of Amidines and Chalcones

Aki Takeda, Hayaki Okai, Kyoji Watabe and Hiroki Iida*

*Department of Chemistry, Graduate School of Natural Science and Technology, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan, Email: iidariko.shimane-u.ac.jp

A. Takeda, H. Okai, K. Watabe, H. Iida, J. Org. Chem., 2022, 87, 10372-10376.

DOI: 10.1021/acs.joc.2c00596



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Abstract

The combination of flavin and iodine catalyzes a facile and atom-economical oxidative cross-dehydrogenative coupling between amidines and chalcones to provide tetra-substituted imidazoles in good yields. The riboflavin-iodine catalytic system played multiple roles in substrate- and O2-activation generating benign H2O as the only byproduct.

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proposed mechanism



Typical Procedure for Catalytic Synthesis of Imidazoles

A mixture of chalcone (1.0 mmol), amidine ( 1.5 mmol, 1.5 equiv), I2 (25.3 mg, 0.10 mmol, 0.1 equiv), TARF (54.4 mg, 0.10 mmol, 0.1 equiv), and PhCl (4.0 mL, 0.25 M) was stirred at 110 °C (oil bath) for 72 h under O2 (1 atm, balloon). Evaporation of the solvent and purification of the residue by column chromatography (SiO2, hexane/CH2Cl2=3/1 to 1/2, v/v) afforded the desired product.


Key Words

imidazoles, organocatalysis


ID: J42-Y2022