Asymmetric Hydrosilylation Of Ketones Catalyzed By Superparamagnetic Recoverable And Reusable Cu-Fe Nanoparticles And Copper-Catalyzed Asymmetric1,4-reduction Of N-Arylβ-Aryl β-Dehydroamino Acid Esters

Chiral secondary alcohols are the key building blocks for the manufacture of many pharmaceuticals, agrochemicals, and advanced materials. Non-presious metal catalyzed asymmetric hydrosilylation towards to enantiomerically enriched secondary alcohols has attrached much attention because of the mild reaction conditions, operational simplicity and cost efficiency. Developing of easy separation, recoverable and reusable heterogeneous chiral catalyst system is one of the effective protocals to improve the catalytic efficiency and to promote the industrialization of chiral catalysis. Nowadays, researches in synthesis of chiral alcohols through asymmetric hydrosilylation mediated by heterogeneous chiral non-presious metal asymmetric catalytic systems are still in the initial stage.Currently, noble metals Rh or Ru catalyzed asymmetric hydrogenation of N-acyl protected β-dehydroamino acid esters is the most efficient strategy leading to optically pure β-amino acid. The development of highly effective chiral non-precious metal catalyst systems for the asymmetric reduction of β-dehydroamino acid esters without N-acyl protection is not only of interest to the academic world but also of substantial interest to industrial scientists.This study focused on the developlepment of both the heterogeneous magnetic nanoparticles CuFe2O4@KIT-6and the homogeneous copper mediated asymmetric hydrosilylation systems and the research results are summarized as followes:(1) Fifteen N-aryl β-aryl β-enamino esters substrates have been synthesized and characterized by1H NMR and13C NMR analysis. Also, the racemic forms of the corresponding fifteen alcohols and fifteen N-aryl β-aryl β-amino esters were prepared and characterized by1H NMR and13C NMR analysis. The chiral analytical methods of these racemic products were established as well.(2) To establish a non-presious heterogeneous catalyst system, which is recoverable and reusable, is one of the emphases of this thesis. We use the superparamagnetic CuFe2O4nanoparticles supported on mesoporous silica KIT-6as the catalyst precursor and combine it with chiral ligands to form the chiral catalysts for the asymmetric hydrosilylation of various ketones. Systematic investigations, various fine-tunings and modifications have been made on counterions of metal precursor, chiral ligands, silanes and additives. The results indicated that in the presence of certain amounts of t-BuONa and t-BuOH as additives, the combination of CuFe2O4@KIT-6, enantiomeric Xyl-P-Phos and an inexpensive and innocuous hydride donor PMHS formed in situ an efficient and practical heterogeneous catalytic asymmetric hydrosilylation system in normal atmosphere.(3) The developed air-stable heterogeneous catalytic system was further applied in the catalytic enantioselective hydrosilylation of a broad assortment of prochiral simple ketones such as aryl alkyl, heteroaryl alkyl, diaryl and α-,β-,y-halo substituted ketones with good to excellent enantioselectivities (ee up to97%) as well as quantitative conversions. The enantioselectivities obtained from the heterogeneous catalyst system were superior to those from the corresponding homogeneous catalyst system, which implied that the spatial confinement effect derived the nano pores of mesoporous materials is beneficial to improve the enantioselectivities.(4) Based on the magnetic property of CuFe2O4catalyst precursor in this heterogeneous catalyst system, we investigate the separation, recoverable and reusable performance of the catalyst. When we use1-(4-bromophenyl)ethanone as the model substrate, the CuFe2O4catalyst was reused for four times with the retention of excellent reactivities and enantioselectivities which shows a good application prospect of this catalyst system.(5) To develope an economic, practical and efficient catalyst system used in the asymmetric hydrosilylation of N-aryl β-aryl β-dehydroamino acid esters is another focus of this thesis. The results indicated that in the presence of certain amounts of CH3ONa and t-BuOH as additives, the combination of CuF2. PMHS and enantiomeric P-Phos generated in situ an efficient catalyst system in normal atmosphere for the asymmetric hydrosilylation of a wide scope of A’-aryl β-aryl β-dehydroamino acid esters with good to excellent ee’s (ee up to95%). This method provides a novel, economic and efficient strategy for the synthesis of chiral N-aryl β-aryl β-amino acid derivative.