Intermolecular versus Intramolecular Palladium-Catalyzed Direct Arylations between 1-(2-Bromobenzyl)imidazoles and Aryl Bromides
Abstract
Herein, we report on the sequential palladium-catalyzed intermol. followed by intramol. direct arylations of 1-(2-bromobenzyl)imidazoles. We found that, in the presence of 1 mol% palladium acetate and potassium acetate as base, the intermol. reaction between 1-(2-bromobenzyl)imidazole derivs. and electron-deficient aryl bromides proceeded faster than the intramol. reaction, allowing us to prep. medium-size polycyclic imidazoles after a second Pd-catalyzed intramol. arylation. These iterative direct arylations allowed the synthesis of fused nitrogen-contg. heterocycles with a 5- or 7-membered-ring in only two steps. Some reactions have also been performed as a one-pot procedure using 2 mol% of palladium acetate in the presence of a larger amt. of base (3 equiv.).