手性有机小分子催化烯胺不对称还原

手性胺是合成天然产物和手性药物的重要中间体，亚胺和烯胺的不对称催化还原是制备手性胺最直接有效的方式之一。手性有机小分子催化的亚胺不对称还原已取得了可喜的进展，但到目前为止，有机小分子催化的烯胺不对称还原，尤其是环状烯胺的不对称还原还少有报道。 本研究从手性叔丁基亚磺酰胺出发，设计并合成了一系列含有叔丁基亚磺酰基的新型脲类及硫脲类催化剂，并将其用于催化三氯硅烷对烯胺的不对称还原，尤其是1, 4-二氢吡啶酯类环状烯胺的不对称还原。通过对催化反应条件的优化，发现当添加1eq H2O时，反应收率和对映选择性明显提高，获得高达99% 的收率和88% ee，同时也取得了很好的非对映选择性（dr = 8:92）。首次实现了三氯硅烷对1, 4-二氢吡啶酯类环状烯胺的高立体选择性还原。 通过机理方面的研究，我们推测反应过程中可能是：首先，底物1, 4-二氢吡啶酯与催化剂形成氢键而被活化，当加入添加剂后，添加剂与三氯硅烷反应释放出一个质子，然后受活化的1, 4-二氢吡啶酯捕获该质子转变成更活泼的亚胺正离子的中间体。随后，在催化剂上的手性硫氧的活化下，三氯硅烷的负氢加成到受活化的亚胺正离子的中间体上，最后生成比较有利的反式产物1, 4, 5, 6-四氢吡啶乙酯。 Calalytic enantioselective reduction of imines and enamines represents one of the most straightforward and efficient methods for the preparation of chiral amines, which is an important class of intermediates for the synthesis of natural products and chiral drugs. Significant progresses have been made in organocatalytic enantioselective reduction of imines. However, asymmetric reduction of enamines, especially of cyclic enamines catalyzed by small organocatalysts has scarcely been reported. In this study, starting from chiral tert-butanesulfinamide, a series of structurally simple tert-butanesulfinyl urea and thiourea organocatalysts were developed and employed in asymmetric reduction of enamines by triclorosilane, particularly in the reduction of cyclic enamines such as Hantzsch 1, 4-dihydropyridines. During the optimization of reaction condictions, we found that the addition of one equivalent of H2O could significantly improve the yields and enatioselectivities. Under optimal condictions, 99% yield, up to 88% ee, and 8:92 diastereomeric ratio were obtained. Thus, we have for the first time realized the highly stereoselective reduction of Hantzsch 1, 4-dihydropyridines catalyzed by triclorosilane. As for the mechanism, we speculate that the Hantzsch 1, 4-dihydropyridine was firstly engaged with the catalyst through hydrogen bond. The proton released from the reaction of the additive and triclorosilane next added to one of the C=C bond to make an active iminium intermediate, which was then attacked by the nucleophlic hydrogen of HSiCl3 activated by the Lewis basic sulfinyl function of the catalyst to provide superior trans-1, 4, 5, 6-tetrahydropyridine products.

Comparison doses of secondary neutron with the heavy ions in a 75-mev/n heavy ion beam

国科图

科尔沁沙地75种植物结种量种子形态和植物生活型关系研究

研究了科尔沁沙地75种植物的结种量、种子形态、植物生活型关系。结果表明,灌木和半灌木(小半灌木)的结种量比草本植物的大;就草本植物而言,多年生植物的结种量较一、二年生植物的小;植物结种量和种子重量之间存在显著负相关;植物结种量和种子形状之间存在显著负相关,即种子越接近圆球形,结种量越大;占绝大多数的草甸植物结种量相对较小;而在物种数占总物种数的百分数相近时,草原植物的结种量最小,沙生植物的最大,杂草植物居中。

High-pressure sintering the novel light (W0.25Al0.75)C hard material without binder phase

A novel hard material of (W0.25Al75)C has been successfully prepared by the high-pressure sintering process without the addition of any binder phase. The high-pressure is a suitable and powerful technique for sintering the binderless hard material, the relative density of the hard material can reach 99.6% under high-pressure sintering. The density of the novel light hard material is only 6.2371 g cm(-3), which is much lighter than the normal hard material. The hardness of the light hard material can reach 18.89 GPa even the aluminum content get the astonished 75%.

Selective hydrogenation of citral with transition metal complexes in supercritical carbon dioxide

The activity and selectivity of the transition metal complexes formed from Ru, Rh, Pd and Ni with triphenylphosphine (TPP) have been investigated for hydrogenation of citral in supercritical carbon dioxide (scCO(2)). High activities are obtained with Ru/TPP and Pd/TPP catalysts, and the overall activity is in the order of Pd approximate to Ru > Rh > Ni. The Ru/TPP complex is highly selective to the formation of unsaturated alcohols of geraniol and nerol. In contrast, the Pd/TPP catalyst is more selective to partially saturated aldehydes of citronellal. Furthermore, the influence of several parameters such as CO2 and H-2 pressures, N-2 pressure and reaction time has been discussed. CO2 pressure has a significant impact on the product distribution, and the selectivity for geraniol and nerol can be enhanced from 27% to 75% with increasing CO2 pressure from 6 to 16 MPa, while the selectivity for citronellol decreases from 70% to 20%. Striking changes in the conversion and product distribution in scCO(2) could be interpreted with variations in the phase behavior and the molecular interaction between CO2 and the substrate in the gas phase and in the liquid phase.

Synthesis, reactive mechanism and thermal stability of W1-xAlxC (x=0.33, 0.5, 0.75, 0.86) nanocrystalline

W1-xAlxC (x = 0.33, 0.50, 0.75, 0.86) solid solutions have been synthesized directly by ball-milling tungsten powder, aluminum powder and activated carbon. The structural development of W0.5Al0.5C phase with the milling times up to 160 h has been followed using X-ray diffraction. X-ray photoelectron spectra demonstrate that Al atom takes the place of W. High temperature annealing experiment reveals that Al is stable in hexagonal structure to 1873 K. Transmission electron microscopy image shows that the grain size of the prepared powders is about 5 nm.

Model 75图象处理系统止软件开发方法的研究

Model 75是一个先进的图象处理机，它大量采用了先进的硬件技术，从而使其具有一般通用机无法相比的强大处理能力。System 575是运行于Model 75上的图象处理软件系统。它有比较完善的图象处理能力，然而System 575却没有一种好的软件开发方法，致使我所购进Model 75以来没能充分利用它的强大能力。针对这种情况，本文探讨了一种能自由运用Model 75的软件开发方法。由于Model 75不同于一般的通用机，因而很好地使用Model 75必须建立在对它的结构有清楚的了解的基础上。本文在大量实验的基础上对Model 75的结构及功能特点做了分析。为验证本人对Model 75的理解和本文所述方法的正确性，本人做了两个较大的实验，一个是运动模糊图象的恢复，一个是道路寻找的可变此值方法。本文介绍了这两个实验。实验表明本文所述的开发方法是有效的，解决了在Model 75上开发软件的难题。