Chiral rhodium(Ⅱ)-catalyzed asymmetric aldol-type interception of an oxonium ylide to assemble chiral 2,3-dihydropyrans

A chiral dirhodium complex is an effective and robust catalyst for asymmetric carbene transformations.However,dirhodiumcatalyzed asymmetric ylide interception processes are rare,mainly because of the dissociation of the metal catalyst before the stereo-determining step.Herein,we report a chiral dirhodium(Ⅱ)-catalyzed asymmetric annulation of vinyl diazoesters withα-hydroxyl ketones,which provides an efficient way to form chiral 2,3-dihydropyrans in good yields with excellent diastereoselectivities and enantioselectivities.This article is the first example of the chiral dirhodium complex–controlled asymmetric aldol-type interception of an in situ–formed oxonium ylide.The origin of the high stereoselectivity is well expounded via experimental and computational studies.These generated chiral products exhibit potent antiproliferation activity in three tested cancer cell lines,namely HCT116(colon cancer),A549(lung adenocarcinoma),and SJSA-1(osteosarcoma cancer).

Enantioselective trapping of oxonium ylide intermediates by N-benzhydryl-α-imino ester：Synthesis of β-tetrasubstituted α-amino acids

A synergistic rhodium（Ⅱ）/phosphoric acid catalyzed three component reaction of 3-diazooxindoles,alcohols and N-benzhydryl-α-imino ester is developed for the efficient construction of chiral β-alkoxy C-β-tetrasubstituted α-amino acid derivatives in good yields and with excellent diastereoselectivities and high enantioselectivities.The synthetic application of the resulting products was illustrated by reducing with Pd/C under H_2 atmosphere followed reacting with CSCl_2 at room temperature to rapid afford 3-spirocyclic oxindole in a good yield with a chirality retainment.The three-component reaction is proposed to proceed through an electrophilic trapping of the oxonium ylides by N-benzhydryl-α-imino ester.

Decomposition of a β-O-4 lignin model compound over solid Cs-substituted polyoxometalates in anhydrous ethanol: acidity or redox property dependence?

Production o f aromatics from lignin has attracted much attention. Because of the coexistence of C-O and C-C bonds and their complex combinations in the lignin macromolecular network, a plausible roadmap for developing a lignin catalytic decomposition process could be developed by exploring the transformation mechanisms of various model compounds. Herein, decomposition of a lignin model compound, 2-phenoxyacetophenone （2-PAP）, was investigated over several ce-sium-exchanged polyoxometalate （Cs-POM） catalysts. Decomposition of 2-PAP can follow two dif-ferent mechanisms： an active hydrogen transfer mechanism or an oxonium cation mechanism. The mechanism for most reactions depends on the competition between the acidity and redox proper-ties of the catalysts. The catalysts of POMs perform the following functions： promoting active hy-drogen liberated from ethanol and causing formation of and then temporarily stabilizing oxonium cations from 2-PAP. The use of Cs-PMo, which with strong redox ability, enhances hydrogen libera-tion and promotes liberated hydrogen transfer to the reaction intermediates. As a consequence, complete conversion of 2-PAP （〉99%） with excellent selectivities to the desired products （98.6% for phenol and 91.1% for acetophenone） can be achieved.

HSAPO-34分子筛上氧鎓叶立德机理的第一性原理研究

采用基于周期性边界条件的密度泛函理论研究了HSAPO-34分子筛上甲醇通过氧鎓叶立德机理直接耦合生成乙烯的可能性.结果表明,二甲醚和三甲基氧鎓离子在HSAPO-34分子筛上的生成能垒分别为1.68和0.93eV,中间体氧鎓叶立德不能稳定存在,同时表明C–C键通过协同反应形成的能垒均超过3.0eV.因此,甲醇制烯烃催化过程不可能遵循氧鎓叶立德机理.

氧(金翁)离子法合成端羟基聚四氢呋喃-聚环氧丙烷嵌段共聚醚

以端羟基聚四氢呋喃（PTHF）和聚环氧丙烷（PPO）大分子为原料，浓硫酸为催化剂，在加热条件下，聚四氢呋喃两端生成鎓离子活性中心，遇到两端含活泼氢的聚环氧丙烷时发生反应，从而制备出了一种全新结构的端羟基PTHF-PPO嵌段共聚醚；通过凝胶渗透色谱（GPC）、红外光谱（IR）和核磁共振（NMR）对产物进行了表征。考察了反应温度、反应时间、催化剂用量等因素对聚合产率以及产物相对分子质量的影响。随着反应温度升高，反应时间的延长，或催化剂用量的增加，共聚醚的产率和相对分子质量都是先增大后减小。研究结果表明，反应温度为120 ℃～130 ℃，反应时间为4h，催化剂用量为PTHF质量的4％时最为理想；共聚醚黏度低，常温下为液态，浇注方便，是生产聚氨酯的很好原料。

Studies on the Interaction of 12-Tungstophosphoric Acid and Diethylene Glycol

The homogeneous system of 12-tungstophosphoric acid and diethylene glycol was studied using IR and NMR spectra. It was found that the protons in 12-tungstophosphoric acid formed proton oxonium ions with the hydroxyl oxygen in diethylene glycol by hydrogen-bonds, and the formed proton oxonium ions could react with the terminal oxygens of heteropoly anions. The dehydration-cyclization mechanism of diethylene glycol in the presence of heteropoly acid was also proposed.

金属催化重氮化合物参与的分子间多组分反应研究进展

本文根据反应历程综述了金属催化重氮化合物参与的分子间MCR的研究进展,经羰基叶立德和亚胺叶立德中间体的1,3-偶极环加成反应是构建四氢呋喃环、1,3-二氧五环、四氢吡咯环等含氧、氮的五元杂环结构的有效方法,具有反应产率高、立体选择性好等特点;经1,2-偶极结构的铵基叶立德和氧鎓叶立德中间体的亲核加成反应能够一步合成重要的有机中间体。

Insertion of O—H Bond of Rh(Ⅱ)-methylene Carbene into Alcohols: A Stepwise Mechanism More Plausible than a Concerted Mechanism

The mechanisms of insertion of O-H bond of Rh（ Ⅱ ）-methylene carbene into methanol and ethanol were studied by using B3LYP functional both in gas phase and in CH2 C12. The formation of free alcoholic oxonium ylides is found to be impossible. Alcoholic oxonium ylide are formed as the intermediates before beth the stepwise and the concerted transition states of insertion of O-H bend of Rh（ Ⅱ ）-methylene carbene into methanol and ethanol. With re- gard to the mechanisms of insertion of O-H of Rh（ Ⅱ ） -methylene carbene into alcohols, analysis of the energy bartiers of the two mechanisms indicate that the stepwise mechanism is more plausible than the concerted mechanism.

氧吲哚生物碱Humantenine关键骨架的立体选择性构建

通过炔锂试剂11与环氮化合物10的区域和立体选择性加成构建了humantenine等钩吻生物碱不对称全合成路线中的重要中间体13;通过酸催化的烯醇-氧环合策略一步构建了humantenine等钩吻生物碱结构中的四氢吡喃环、环氧己烷、C7季碳中心和C3手性中心;最终从已知化合物7出发,以16步1.5%的总收率完成了humantenine(2),humantenine N4-oxide(3),gelseganines A(4)和gelseganines B(5)等钩吻生物碱关键中间体化合物6的不对称合成.

铀酸铵的沉淀机理和工艺选择

ＵＯ￣（２＋）＿２离子水解形成铀酸铵，以双核为主的水解络离子进一步水解聚合生成亚稳态的氢氧化铀酰。后者的结构中存在着键，溶液中存在的中性电解质的阳离子能与键上的氢发生替代反应，经聚合歧化形成沉淀物铀酸铰（ＡＤＵ）。铀酸铵片晶小．易面面吸附形成颗粒，均匀的小颗粒进一步聚集成松散的团粒。转化Ｆ￣－体系成体系，或严格控制ｐＨ值，采用两步法沉淀，加速ＡＤＵ的成核速率，可以制备出特性化ＵＯ＿２粉末所需的铀酸铵。

Rh_2(OAc)_4-AuCl_3协同催化三组分串联反应高效构建异色烯衍生物

多组分串联反应能从简单原料实现复杂目标化合物的快速、高效合成,最大限度地提高了反应效率.本文研究了重氮化合物、醇以及邻炔基芳醛的三组分串联反应,通过Rh2(OAc)4与AuCl3协同催化,成功实现了单催化策略不能发生的反应,一步高效构建了多官能团异色烯骨架并且反应有较好的化学选择性和中等至较好的非对映选择性.