Studies On The Asymmetric Amidocarbonylation Reaction And Homocoupling Reaction Of Terminal Alkynes

This dissertation was focused on two different types of catalytic reactions. Asymmetric amidocarbonylation reaction and homocoupling reaction of terminal alkynes were explored, respectively.Optically pureα-amino acid and its derivatives have great potential applications in pharmaceutical industry and organic synthesis. Amidocarbonylation is a facile and effective method for the preparation of N-acyl-α-amino acids. However, Palladium catalysts are expensive and unrecoverable; Asymmetric amidocarbonylation has not been achieved successfully, only racemic N-acyl amino acids were formed via amidocarbonylation. In order to recycle the catalytic system and obtain optical amino acids and their derivatives, the investigations were undertaken in the following two aspects.The homogeneous catalyst system (PdBr₂/PPh₃/LiBr/H₂SO₄/NMP) developed by Beller etc. for amidocarbonylation was improved in the present study. Two types of ionic liquids (halide anion ionic liquids and Brφnsted acidic ionic liquids) were first applied to improve the palladium-catalyzed amidocarbonylation. Halide anion ionic liquids were used as both the solvent and halogen source; environmentally friendly Brφnsted acidic ionic liquids played a role of strong acid co-catalyst. Both the palladium catalyst and the ionic liquids could be recycled at least five times without significant loss in catalytic activity. This novel protocol exhibits economical and environmentally benign and shows potential utility in industrial applications.Different kinds of phosphine ligands were carefully prepared to try asymmetric synthesis in amidocarbonylation reactions. Unfortunately the most experiments were essentially failured in our laboratory. Based on the analysis of reported reaction mechanism of amidocarbonylation it was found that the occurrence of asymmetric induction on the carbon atom of carbonyl group of aldehydes was very difficult. Meanwhile the undesired racemization of target product would be an other obstacle for the asymmetric synthesis in amidocarbonylation. An alternative way was attempted via asymmetric hydroesterification of enamide and N-acyl imine in the presence of chiral ligands. In the case of N-vinylphthalimide as the substrate, 12.3% ee in the optical yields was obtained by using (S)-(+)-BNPPA as the chiral ligand.Alkyne dimerization to give 1, 3- diynes through oxidative homocoupling, so-called Glaser coupling reaction, is important for a number of applications, particularly in the construction of linearlyÏ€-conjugated acetylenic oligomers and polymers, natural products, and molecular recognition processes. The commonly used catalyst system for the oxidative homocoupling coupling reaction was the Pd-catalyzed system, which involved Cu (â… ) salts as co-catalyst. Although the Pd-catalysts were effective for conducting the homocoupling reaction of terminal alkynes, they were much more expensive than the easily available cupric salts and often required phosphine or amine reagents. For the copper-catalyzed Glaser coupling reaction, copper (â… ) salt was commonly used. Cu (â…¡) salts catalyzed oxidative acetylenic coupling proved of great value since its discovery, but didn't gain much attention. In the present study, the preparation and characterization of Cu (â…¡) -containing hydrotalcites and their use as catalyst for Glaser coupling reaction were reported. It is for the first time that CuAl-LDH was developed as effective homocoupling coupling catalyst and this catalyst could be reused for eight cycles with consistent reactivity. This procedure could avoid the handling of expensive palladium catalysts and sensitive Cu (â… ) salts. The extremely mild experimental conditions, low cost and reusability of CuAl-LDH catalyst constructed a green strategy for the synthesis of 1, 3-conjugated diynes with great potential for commercial applications.