Copper-catalyzed Stereoselective Synthesis Of (E)-Dibromoalkenes From Alkynes

Alkynes containing a carbon-carbon triple bond is a kind of important organic fu nctional group, which is commercial available, cheap and easy to obtain. Therefore, they have been widespread applied in organic synthesis and were involved in importan t organic transformation including the formation of C-C, C-X, C-O, C-N bond. At the same time, they have been highly favored by chemists in organic synthesis, which applied to all directions in the field of organic synthesis. Therefore, deeply studies and development concerning on carbon-carbon triple bond-related learn ing still remained desrible.This thesis is concerned on the formation of C-X bond and C-O bond using alkyn es as raw material. It is divided into three parts as follows:1. Dihaloalkenes is one of the important structural units in organic synthesis, their synthesis is very useful. A general method for the synthesis of various（E）-Dibromoalkenes has been developed. We have examined the impact of the bromide agent, catalyst and solvent respectively by establishing a model reaction using phenylacetylene as the substate, and obtained the optimum reaction conditions. The reaction proceeded efficiently in the presence of 2.0 equiv Cu Br 2, 5.0 mg 4? molecular sieves and anhydrous acetonitrile under room temperat ure. The corresponding products were prepared after concentration and purification by chromatography. Mechanistically, this method produced a variety of（E）-Dibromoalkenes with the advantages of mild reaction conditions.2. With the optimal conditions in hand, we embarked on the evaluation of the substrate scope for this transformation. To our delight, this method was suitable for aromatic alkynes, aliphatic alkynes as well as heterocyclic alkynes. Notably, the internal alkyne, which was usually much less reactive than the terminal alkyne, was also available. Meanahile, various functional groups were tolerated. Futhermore, based on experimental data in the laboratory and related literature, a possible mechanism was proposed to explain the reaction mechanism. 3. β-Ketophosphonates represent an important class of carbonyl compounds that are found in a variety of biologically active molecules. They also act as key building blocks in organic synthesis. However, traditional methods for β-Ketophosphonates suffer from several shortcomings. Therefore, we report a simple and efficient way to β-ketophosphonates. A large number of β-ketophosphonates were easily prepared via Ag NO₃-catalyzed hydration of alkynylphosphonates with a dramatic rate-enhancement effect of methanol. This benign aqueous-methanol method catalyzed by a low-cost catalyst has simple, atom-economical procedure, and 24 species β-ketophosphonates were prepared.