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91.
Mechanism of Phosphine‐Catalyzed Allene Coupling Reactions: Advances in Theoretical Investigations 下载免费PDF全文
Dr. Cheng‐Xing Cui Dr. Chunhui Shan Prof. Yu‐Ping Zhang Prof. Xiao‐Lan Chen Prof. Ling‐Bo Qu Prof. Yu Lan 《化学:亚洲杂志》2018,13(9):1076-1088
Organocatalysis has emerged as an effective strategy for chemical synthesis. Within this area, phosphine‐catalyzed coupling reactions have attracted considerable attention because of their versatility and wide range of applications in the construction of new C?C bonds. Recently, various experimental studies on the phosphine‐catalyzed coupling reaction of allenes have been reported, and mechanistic and computational studies have also progressed considerably. As a nucleophile, phosphine can react with an allene to form a zwitterionic phosphoniopropenide intermediate. After stepwise cycloaddition and proton transfer, the phosphine catalyst can be regenerated by C?P bond cleavage. Alternatively, the zwitterionic phosphoniopropenide intermediate could also be protonated by a Brønsted acid to generate a phosphonium intermediate, which can be used to construct new C?C bonds by electrophilic addition. In this review, we have summarized details of mechanistic studies of phosphine‐catalyzed allene coupling reactions that follow these two reaction modes. In addition to detailing the reaction pathway, the regioselectivity and diastereoselectivity of the phosphine‐catalyzed allene coupling reaction are also discussed in this review. 相似文献
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Chaojun Deng Haoyuan Wang Hongqiang Lan Boya Xu 《Journal of Dispersion Science and Technology》2018,39(11):1582-1587
The flow behavior in a three-phase separator with a bucket and weir was analyzed, and a theoretical equation for calculating the liquid-liquid interface level (HH) in gravity separation zone was derived. The analysis indicates that the HH increases as the flow rate and the density ratio of heavy to light liquid increase, and decreases linearly with increasing height difference between heavy and light liquid overflow weirs. The calculated HH under different operating conditions is in good agreement with the experimental. With the proposed equation, the thicknesses of heavy and light liquid layers can be calculated, and then the minimum lengths of two phase layers required for separation can be determined separately. From the minimum lengths it can be clearly indicated that the governing step of liquid-liquid separation is in heavy or light liquid layers, hence the sizing of the separator can be optimized. 相似文献
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The direct Pd-catalyzed β-C(sp3) H activation and cyclization of aliphatic amides bearing a removable 2-pyridylmethyl directing group with gem-dibromoolefins is described for the first time to construct a variety of γ-lactams. 相似文献
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Y. C. Lan X. L. Chen A. Y. Xie P. Z. Jiang C. L. Lin 《Journal of Crystal Growth》2002,240(3-4):526-530
This paper reports the detail synthesis of a new kind of metal iodate, anhydrous (LiFe1/3)(IO3)2, from aqueous solutions. The synthesized compound shows spinal morphology and is chemical stable up to 400°C. The iodate shows paramagnetic behavior from room temperature down to 4.2 K. At room temperature, the new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1, space group of P63. 相似文献
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本文采用原子力显微镜(AFM)和XRD研究了生长在蓝宝石(11-02)基片上的CeO_2缓冲层在不同的退火温度和退火时间下表面形貌和相结构的变化,以及对Tl-2212薄膜超导特性的影响.AFM和XRD研究表明,CeO_2薄膜在流动氧环境中退火,表面形貌发生显著的变化;CeO_2薄膜在最佳条件下退火后,可获得原子级光滑表面,结晶质量明显提高.实验结果表明,缓冲层的结晶质量和表面粗糙度与Tl-2212薄膜的超导特性密切相关.在经过最佳条件退火后的CeO_2缓冲层上制备了厚度为500 nm无裂纹的Tl-2212超导薄膜,其临界转变温度(T_c)达到107 K,液氮温度下临界电流密度(J_c)为3.9 MA/cm~2(77 K,0 T),微波表面电阻(R_s)约为281 μΩ(77 K,10 GHz). 相似文献
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