Optically active a-arylalkylamines are an important class of compounds that are widely used in organic and pharmaceutical synthesis, and much effort has been made to develop efficient asymmetric synthetic methods for them. [1] Asymmetric catalytic hydrogenation of enamides, initiated by Kagan et al., [2] provides a direct and convenient route to chiral amine derivatives. However, many well-known chiral diphosphane ligands, such as DIOP, BINAP, and CHIRA-PHOS, which are extremely successful in the asymmetric hydrogenation of dehydroamino acid derivatives, do not give high enantioselectivity in the hydrogenation of enamides. [3,4] A breakthrough was achieved by Burk et al. [4a] with the introduction of BPE and DuPHOS ligands, which gave excellent enantioselectivity in the Rh-catalyzed asymmetric hydrogenation of enamides. Lately, some other P ligands were also reported to be efficient in the hydrogenation of enamides. [4b, 5] However, all ligands that gave a high degree of enantiocontrol are bidentate. To our knowledge, no efficient chiral monodentate ligand has been reported for the asymmetric hydrogenation of enamides, although some monodentate P ligands were successfully used in the hydrogenation of dehydroamino acid derivatives. [6] Here we describe highly efficient monodentate chiral ligands 1 containing a 1,1'-spirobiindane backbone for the Rh-catalyzed asymmetric hydrogenation of a-arylethenylamine derivatives [Eq. (1)] with excellent enantioselectivities (up to 99.7 % ee).The chiral monodentate phosphoramidite ligands 1 (abbreviated SIPHOS) were conveniently synthesized in good yields from enantiomerically pure 1,1'-spirobiindane-7,7'-diol, which was easily prepared from 3-methoxybenzaldehyde by using the procedure described by Birman et al. [7] We demonstrated recently that the Rh complex of (S)-1 a (R CH 3 ) is a highly efficient catalyst in the asymmetric hydrogenation of dehydroamino acid and itaconic acid derivatives with up to 99.3 % ee. Therefore, we were prompted to investigate the utility of this catalyst in the asymmetric hydrogenation of a-phenylenamide 4 a and an excellent enantioselectivity (up to 98.8 % ee) was achieved. This showed, for the first time, that monodentate phosphorus ligands can be effective in the enantiocontrol of asymmetric hydrogenation of enamides.The results in Table 1 show that the enantioselectivity of the reaction was sensitive to the solvent used, and toluene is the solvent of choice. In contrast, the hydrogen pressure has a negligible influence on the enantioselectivity. For example, in the hydrogenation of 4 a with Rh/(S)-1 a catalyst in toluene, the ee values of product 5 a at 25 8C under 10 atm and 100 atm H 2 were 96 % and 96.2 %, respectively (Table 1, entries 1 and 2). The investigation of catalyst loading showed that 0.5 mol % catalyst was sufficient to give a high enantioselectivity, while the ee value of the product dropped drastically with 0.1 mol % catalyst.Catalysts prepared in situ from cationic Rh complexes were active in the asymmetric hydrogenation...
By using the recently developed Thomson scattering diagnostic, the pedestal structure of the H-mode with neutral beam injection (NBI) or/and lower hybrid wave (LHW) heating on EAST (Experimental Advanced Superconducting Tokamak) is analyzed in detail. We find that a higher ratio of the power of the NBI to the total power of the NBI and the lower hybrid wave (LHW) will produce a large and regular different edge-localized mode (ELM), and a lower ratio will produce a small and irregular ELM. The experiments show that the mean pedestal width has good correlation with β p , ped 0.5 , The pedestal width appears to be wider than that on other similar machines, which could be due to lithium coating. However, it is difficult to draw any conclusion of correlation between ρ * and the pedestal width for limited ρ * variation and scattered distribution. It is also found that T e/ ∇ T e is ~2 cm, which is the same as the AUG (ASDEX Upgrade), DIII-D and JET (Joint European Torus) results.
Novel monodentate phosphorus ligands containing the 1,1'-spirobiindane backbone have been synthesized and applied in the asymmetric rhodium-catalyzed hydrogenation of functionalized olefins, providing excellent enantioselectivities (up to 99.3% ee).
Recent experiment results from the HL-2A tokamak are presented in this paper. Supersonic molecular beam injection (SMBI) with liquid nitrogen temperature propellant is used. Low temperature SMBI can form hydrogen clusters that penetrate into the plasma more deeply and efficiently. Particle diffusion coefficient and convection velocity (D = 0.5–1.5 m2 s−1 and Vconv < 40 m s−1, respectively) are obtained at the plasma periphery using modulated SMBI. Multi-probe measurements reveal the m = 0–1, n = 0 symmetries of directly measured low frequency (7–9 kHz) electric potential and field are simultaneously observed for the first time. Impurity transport is determined with the laser blow-off system and transport code. A disruption predictor has been derived based on MHD activity observations and statistical analysis. Sawtooth characteristics during ECRH are investigated and coupling between m = 1 and m/n = 2/1 modes is studied. Detachment features of HL-2A divertor are numerically and experimentally studied using the code SOLPS5.0 and measured data. The long divertor legs and thin divertor throats in HL-2A pose MHD shaping problems resulting in momentum losses even at low densities and strongly enhanced main chamber losses.
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