10.1021/ol901684h
The research explores an efficient method for the direct C-H alkynylation of azoles using alkynyl bromides in the presence of a nickel-based catalyst system. The study investigates the effects of various ligands, solvents, and reaction conditions to optimize the yield of the alkynylation products. Key chemicals involved include benzoxazole and various alkynyl bromides such as (bromoethynyl)benzene, which serve as the substrates. The nickel catalysts, specifically Ni(cod)2 and Ni(acac)2, play crucial roles in facilitating the reaction, with the addition of ligands like 1,2-bis(diphenylphosphino)benzene (dppbz) significantly enhancing the catalytic activity. Lithium tert-butoxide (LiO-t-Bu) is used as a base to deprotonate the azoles, generating heteroaryllithium intermediates essential for the transmetalation step. In some cases, a catalytic amount of CuI is added to further accelerate the reaction, suggesting the possible formation of heteroarylcopper species that facilitate the coupling process. The optimized conditions enable the introduction of a wide range of alkynyl groups bearing different substituents to the azole cores, demonstrating the synthetic utility of this transformation for creating complex molecular structures.
