Design, Synthesis And Application Of Chiral N, P-ligand Modified Iridium Catalysts

Asymmetri hydrogenation of alkenes represent a very reliable method for preparation of enantio-enriched organic compounds, and the research on this topics had been awarded as the Nobel prize in Chemistry. Now, this conversion is employed in manufacturing the drug L-DOPA. The key point for the asymmetric hydrogenation is to find a suitable chiral catalyst. Though many chiral catalysts had been developed for the hydrogenation, none of them could be effective for all kinds of substrates. Therefore, the synthesis of a cheap and effective catalyst with wide universality is the permanent objective of organic chemists. This thesis is composed by three sections, and the research contents includes two parts:1. Design and synthesis of chiral iridium catalysts modified by the N,P-ligands; 2. Application of the chiral iridium catalysts in the asymmetric hydrogenation of silyl alkenes. They are listing as follows:In the first part, a brief review on the asymmetric hydrogenation of alkenes was addressed. We described the recent progresses on the chiral Rh and Ru catalyzed hydrogenation of functionalized alkenes, and the chiral Ir-catalyzed hydrogenation of non-functionalized alkenes.In the second part, we carried the research on the design and synthesis of the N,P-ligands. First, the backgrounds of the chiral N.P-ligands were reminded. On the basis of the literature, the project on the synthesis of the N,P-ligands was proposed to fulfill the ligand library. The preparation of the Pfaltz’s N,P-ligands was started from cheap α-amino acids. The L-threonine was acidified by thionyl chloride, and then it was followed by amidation with acyl chlorides. The resulting intermediates proceeded with ring-close of oxazoline, nucleophilic addition of ester by Grignard reagents and O-alkylation with the phosphorus chlorides, producing the 3 desired N,P-ligands. Finally, Two chiral iridium catalysts modified by the N,P-migands were prepared.In the last part, the application of the chiral Iridium catalysts was performed. Asymmetric hydrogenation of the silyl alkenes had been explored, and the chiral catalysts were scanned. Meanwhile, the reaction conditions including the temperature, solvents and the pressure of hydrogen were optimized. Eight optically active silanes with good to excellent enantioselectivity (66-99% ee) and yield (74-99%). While this type of silyl alkenes were reported to be very difficult to be reduced with an excellent control of stereochemistry.