Rhodium(III)‐Catalyzed Selective Direct Olefination of Imidazoles

Abstract

AbstractRhodium(III)‐catalyzed chelation‐assisted highly regio‐ and stereoselective direct olefination of imidazoles with olefins has been developed. A broad range of C2‐substituted N‐(2‐pyrimidyl)imidazoles underwent smooth C5‐olefination with both activated and unactivated olefins to furnish the corresponding products in good to excellent yields with high tolerance of functional groups on both coupling partners in the presence of a cationic rhodium(III) catalyst. The combination of a catalytic amount of Cu(OAc)2 (copper(II) acetate) and O2 (oxygen) serves as the terminal oxidant. This protocol strongly relies on the use of 2‐substituted imidazoles as the substrates, and the presence of readily installable and removable pyrimidyl directing group was found to be critical for catalysis. Mechanistic studies suggest the involvement of a five‐membered rhodacycle as the key intermediate in the catalytic cycle. The method can also be extended to the coupling reaction of benzimidazoles with olefins.magnified image