Copper-Catalyzed Dimerization Reactions Of Terminal Alkynes

The dimerization reaction of terminal alkynes is an important method for the synthesis of the conjugated diynes, conjugated enynes and conjugated dialkenes. As an efficient C-C bond-formation method, the corresponding products-conjugated diynes play an important role as building blocks in many synthetic transformations, and in new materials such as conjugated oligomers and polymers, liquid crystals, non-linear materials, molecular wires, and in other emerging materials. Several symmetrical1,3-diynes have been used exclusively as substitutes to other functional groups in synthetic organic chemistry. In addition, these1,3-diynes are common structural motifs found in numerous natural products, pharmaceuticals and bioactive compounds with antiinflammatory, antifungal, anti-HIV, antibacterial or anticancer activities. Over the past140years, a significant number of catalyst systems have been devoloped for these reactions, which include palladium, nickel, copper, cobalt, and gold catalyst systems. Among them, the copper-mediated Glaser-type coupling reactions represent the most promising methods for the synthesis of1,3-diynes due to its economy and environ-mental friendness. However, the current copper-catalytic systems usually required stoichiometric amount of copper salts, excessive oxidants, poisonous ligands and high reaction temperature, or expensive ionic liquid and supercritical CO2. Therefore, developing new copper-based promoting systems for the mild Glaser-type coupling reaction are highly desirable. The contents of this dissertation mainly reported the copper-catalyzed dimerization reactions of terminal alkynes.Ethyl a,a-dibromoacetoacetate as a novel oxidant, that efficiently promotes the homo-coupling of terminal alkynes. There are numerous versions of the original procedure developed by Glaser, and these differ mainly in the type and amount of oxidants used. More and more novel oxidants were explored and used in this coupling reactions, espically halides, for example, chloroacetone and ethyl bromoacetate, which were employed as efficient oxidants for the Glaser-type coupling. However, palladium catalysts are essential to these methodologies. Therefore, we reported a series of more reactive oxidants, α,α-dibromo-β-dicarbonyl compounds, that allow the homo-coupling of terminal alkynes proceeding with catalytic amount of CuI in air at room temperature without expensive and air-sensitive palladium complex as co-catalyst. It was found that the catalytic system showed good substrate compatibility with various aromatic and aliphatic alkynes, providing the corresponding homo-coupling products in good to excellent yields. Meanwhile, treatment of different terminal alkynes afforded moderate yields. Finally, to gain some understanding of the mechanism, preliminary studies were caried out and three tentative pathways for the reaction were proposed.