A variety of acyclic chiral dienes were synthesized in a single step via palladium(0)-catalyzed asymmetric allylic and homoallylic C À H di-A C H T U N G T R E N N U N G amination of terminal olefins. The applications of such simple dienes as steering ligands for rhodi-A C H T U N G T R E N N U N G um(I)-catalyzed asymmetric 1,4-additions afforded the corresponding adducts in excellent yields and up to 85% ee.Keywords: acyclic chiral dienes; asymmetric catalysis; asymmetric diamination; conjugated addition; diene ligands Chiral olefins have proven to be excellent steering ligands for asymmetric catalysis, and some of them even exhibit a distinct advantage over other types of ligands to afford higher reactivities and/or enantioselectivities. [1,2] With lots of effort devoted to this lately emerging area, a few fantastic chiral chelating diene ligands bearing bicyclic frameworks have been successfully developed. [3][4][5][6] The bicyclic structures of these ligands play a crucial role in the asymmetric reactions, but also partially result in some difficulties in ligand synthesis. Hence, exploring novel, effective, and accessible chiral dienes is still one of the most important subjects in this field.[2b] Inspired by the fact that 1,5-hexadiene (1) has an ability to act as a steering ligand, very recently, we reported that a simple chiral acyclic diene 2 (Scheme 1) can be employed as an effective ligand for promoting Rh(I)-catalyzed asymmetric 1,4-additons with encouraging yields and ees (Scheme 2), [7,8] which demonstrates that the complexes formed between Rh and a flexible diene are stable enough to ensure asymmetric induction.[9] Because of the convenient synthesis, chiral acyclic dienes have the potential to become a class of promising ligands in the future. Herein, we wish to report our efforts on this subject.In our previous work, when two hydroxy groups were introduced into the achiral 1,5-hexadiene skeleton, a simple chiral chain diene ligand 2 was successfully achieved, which suggests that other types of chiral dienes containing 1,5-hexadiene skeletons are also candidate ligands. We envisioned that introduction of imidazolidin-2-one backbones to 1,5-hexadiene may provide a good opportunity to develop novel diene ligands (3) for asymmetric catalysis (Scheme 1).[10] The combination of flexible terminal olefins and rigid imidazolidin-2-one frameworks in ligand 3 and how it might affect asymmetric induction is interesting. Therefore, building the chiral imidazolidin-2-one frameworks became one of the key points.
A kinetic resolution of hindered Morita-Baylis-Hillman adducts has been successfully achieved in excellent selectivities via Rh(I)-catalyzed asymmetric 1,4-addition/β-hydroxyelimination with the use of a chiral sulfinamide/olefin hybrid ligand. This study provides a novel and efficient access to both optically active hindered highly functionalized alkenes and Morita-Baylis-Hillman adducts.
Levulinic acid and its esters (e.g., ethyl levulinate, EL) are platform chemicals derived from biomass feedstocks that can be converted to a variety of valuable compounds. Reductive amination of levulinates with primary amines and H2 over heterogeneous catalysts is an attractive method for the synthesis of N-alkyl-5-methyl-2-pyrrolidones, which are an environmentally friendly alternative to the common solvent N-methyl-2-pyrrolidone (NMP). In the present work, the catalytic properties of the different nickel phosphide catalysts supported on SiO2 and Al2O3 were studied in a reductive amination of EL with n-hexylamine to N-hexyl-5-methyl-2-pyrrolidone (HMP) in a flow reactor. The influence of the phosphorus precursor, reduction temperature, reactant ratio, and addition of acidic diluters on the catalyst performance was investigated. The Ni2P/SiO2 catalyst prepared using (NH4)2HPO4 and reduced at 600 °C provides the highest HMP yield, which reaches 98%. Although the presence of acid sites and a sufficient hydrogenating ability are important factors determining the pyrrolidone yield, the selectivity also depends on the specific features of EL adsorption on active catalytic sites.
A series of metal phosphides were prepared by temperature programmed reduction and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), 31 P magic angle spinning nuclear magnetic resonance ( 31 P MAS NMR), ammonia temperature programmed desorption (NH 3 -TPD) and pyridine infrared spectroscopy (Py-IR), their catalytic performance were investigated in the hydrodeoxygenation of furfural to form 2methylfuran. The effects of metal phosphide and the initial P/Ni molar ratios on the hydrodeoxygenation of furfural were studied, and the reaction conditions were optimized. Furfural was thoroughly converted when the reaction was carried out under 240 8C and 2.0 MPa for 4 h over MoP or Ni 2 P, and the selectivity of 2-methylfuran was achieved 83.1% when the Ni 2 P_0.5 was employed as a catalyst. Under the optimal reaction conditions, the Ni 2 P_0.5 catalyst could be used for six times with slightly decrease in catalytic performance.
Industrial processes of fixing carbon dioxide (CO 2) lag far behind the carbon emission generated by human activity. Since CO 2 is an abundant, non-toxic, and cost-effective one carbon source, it is highly desirable to develop methodologies on converting CO 2 into valuable products for sustainable purpose. Based on the mechanistic insight of CO 2 activation by transition-metal catalyst and organocatalyst, a variety of efficient asymmetric CO 2 chemical fixation processes have been developed in recent years. This review discusses the advances of enantioselective synthesis of small molecules by asymmetric catalytic reactions with CO 2. The interaction between catalyst, CO 2 and substrate has been elaborated aiming to inspire the design of new catalytic systems for asymmetric CO 2 transformation.
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