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.
10.1039/b820879d
1,2-bis(diphenylphosphino)benzene (DPPBz) is a key ligand used to modulate the iron-catalyzed cross-coupling reactions between polyfluorinated arylzinc reagents and alkyl halides. DPPBz plays a crucial role in enhancing the reactivity and selectivity of the iron catalyst. Specifically, it suppresses undesired side reactions such as C-F bond cleavage and E2-elimination, which are common issues in conventional iron-catalyzed cross-coupling reactions involving polyfluorinated aryl metals. By using a catalytic amount of DPPBz, the researchers achieved high yields of the desired coupling products (up to 93%) and minimized the formation of by-products. The ligand's ability to form a stable complex with iron is believed to create a catalytically active species that facilitates the selective cleavage of sp3-carbon–halogen bonds. This selective iron-catalyzed fluoroaromatic coupling provides an efficient and practical method for synthesizing polyfluorinated aromatic compounds, highlighting DPPBz as a vital component in this innovative synthetic approach.
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