α-三唑基查尔酮与苯肼的加成-关环反应研究

（Ｚ）或（Ｅ）－１，３－二芳基－２－（１Ｈ－１，２，４－三唑－１－基）－丙烯－１－酮与苯肼在醋酸中反应均生成顺式和反式吡唑啉异构体混合物，但在在三乙胺催化下却只生成反式的异构体。制备了三对顺、反式的１－苯基－３，５－二芳基－４－（１Ｈ－１，２，４－三唑－１－基）－２－吡唑啉衍生物，其结构为＾１Ｈ ＮＭＲ和元素分析证实，初步论证了经α－氮原子的加成－环化反应机理。

Recent advances in metal-free catalysts for the synthesis of cyclic carbonates from CO_2 and epoxides

The aim of ＂green chemistry＂ and ＂atom economy＂ is to utilize carbon dioxide and replace harmful reactants such as CO and phosgene for the production of cyclic carbonates. In this paper, metal-free catalysts including organic bases, ionic liquids, supported catalysts, organic copolymers and carbon materials for the synthesis of cyclic carbonates by the cycloaddition of carbon dioxide to epoxides are reviewed. Recent advances in the design of the catalysts and the understanding of the reaction mechanism are summarized and discussed. The synergistic effects of organic bases and hydrogen bond donors, organic bases and nucleophilic anions, hydrogen bond donors and nucleophilic anions and active components and supports are highlighted. The challenge is to develop metal-free catalysts suitable for carbon dioxide capture and fixation. The ultimate goal is to synthesize cyclic carbonates in a flow reactor directly using carbon dioxide from industrial flue gas at ambient temperature and atmospheric pressure. By using synergetic effects, a multi-functional approach can meet the design strategy of metal-free catalysts for carbon dioxide adsorption and activation as well as epoxide ring opening.

α-卤代酰胺参与的氮杂环构建方法研究进展

杂环化合物在医药、农药、材料和精细化工品等许多领域发挥着重要作用,因此,开发新颖、有效的合成策略构建杂环化合物一直是人们关注的重点.重点介绍了2011~2020年间α-卤代酰胺原位产生氮氧烯丙基阳离子通过[3+m]-环加成/环化反应构建含氮杂环化合物的最新进展.

Mechanistic Investigation on Rhodium(III)-Catalyzed Cycloaddition of 2-Vinylphenol Derivatives with Ethyne or Carbon Monoxide by DFT Study

Rhodium-catalyzed cycloaddition reaction was calculated by density functional theory M06-2X method to directly synthesize benzoxepine and coumarin derivatives.In this work,we conducted a computational study of two competitive mechanisms in which the carbon atom of acetylene or carbon monoxide attacked and inserted from two different directions of the six-membered ring reactant to clarify the principle characteristics of this transformation.The calculation results reveal that:(i)the insertion process of alkyne or carbon monoxide is the key step of the reaction;(ii)for the(5+2)cycloaddition reaction of acetylene,higher energy is required to break the Rh−O bond of the reactant,and the reaction tends to complete the insertion from the side of the Rh−C bond;(iii)for the(5+1)cycloaddition of carbon monoxide,both reaction paths have lower activation free energy,and the two will generate a competition mechanism.

N-tosyl-nitropyrroles as Dienophiles in Polar Cycloaddition Reactions Developed in Protic Ionic Liquids

N-tosyl-2-nitropirrole and N-tosyl-3-nitropirrole reacts with poorly and activated dienes using protic ionic liquids as reaction media. They exhibit a dienophilic character producing the corresponding indoles through a Diels-Alder process. In all cases the presence of protic ionic liquids as reaction media improve the yields respect to the use of molecular solvent, while the temperature and the reaction time decrease. A similar behavior was observed in disubstituted N-tosyl-pyrroles.

Ionization of a covalent organic framework for catalyzing the cycloaddition reaction between epoxides and carbon dioxide

Covalent organic frameworks(COFs),with two dimensional(2D-)or three dimensional(3D-)structures,have accessible open channels or nanopores,with uniform sizes ranging from angstroms to nanometers and have emerged as an excellent and promising platform for designing catalysts or catalyst carriers.Herein,a 2 D-COF grafted with a 1-alkyl-3-methylimidazolium-based ionic liquid(AMIMBr@H2 P-DHPh COF)on the channel walls was synthesized and utilized as a highly efficient heterogeneous catalyst for the chemical fixation of CO2 via a reaction with epoxides under solvent-free and co-catalyst-free conditions.The as-synthesized AMIMBr@H2 P-DHPh COF shows excellent catalytic activity in promoting the cycloaddition reactions between epoxide and CO2;the excellent catalytic activity was maintained for up to five cycles.Advantages like high porosity,functional versatility,easy modification of COFs,and high catalytic activity of ionic liquids,have been realized in a single material.

Recyclable bifunctional aluminum salen catalyst for CO2 fixation:the efficient formation of five-membered heterocyclic compounds

A variety of unique Al(salen) complexes functionalized by imidazolium-based ionic liquid(IL) moieties with the salen ligand at the two sides of 3,3′-position have been successfully prepared, rather than familiar 5,5′-position reported previously.The catalytic activity obtained by these bifunctional catalysts could be superior to those of the binary type catalysts in the formation of five-membered heterocyclic compounds from the cycloaddition reaction of CO_2 and three-membered heterocyclic compounds(including terminal epoxides and N-substituted aziridines), presumably due to the distinguished intramolecularly synergistic catalysis, which might lead to perform the cycloaddition reaction at ambient conditions and retain excellent yield and unprecedented chemo-or regioselectivity. Moreover, the polyether-based trifunctional Al(salen) catalysts with the best catalytic performance could be regenerated and reused at least eight times without any obvious decreases in catalytic activity. Finally,the kinetic investigation suggested the structure of catalysts had important influences on the catalytic activity, thereby proposing the possible reaction mechanism.

Reaction mechanism and chemoselectivity of gold(Ⅰ)-catalyzed cycloaddition of 1-(1-alkynyl) cyclopropyl ketones with nucleophiles to yield substituted furans

The mechanisms of gold（I）-catalyzed cycloaddition of 1-（1-alkynyl） cyclopropyl ketones with nucleophiles have been investi- gated using density functional theory calculations at the B3LYP/6-31G （d, p） level of theory. A polarizable continuum model （PCM） has been established in order to evaluate the effects of solvents on the reactions. The results of the calculations indicate that the first step of the catalytic cycle is the cyclization of the carbonyl oxygen onto the triple bond which forms a new and stable resonance structure of an oxonium ion and a carbocation intermediate. The subsequent ring expansion step results in the formation of the final product and regeneration of the catalyst. Furthermore, the regioselectivity and effect of substituents has been discussed, including an analysis of energy, bond length, and natural bond orbital （NBO） charge distributions in the rate-determining step. Our computational results are consistent with earlier experimental observations.

Chiral metal-containing ionic liquid:Synthesis and applications in the enantioselective cycloaddition of carbon dioxide to epoxides

A series of novel chiral metal-containing ionic liquids (CMILs) consisting of the cation of crown ether-chelated potassium/ sodium and the anion of chiral amino acids were designed and synthesized. These new CMILs were used to catalyze the enantioselective cycloaddition of epoxides and carbon dioxide incorporating with the salenCo(OOCCC13) to generate corresponding chiral cyclic carbonates under mild conditions. These new catalysts can be recycled at least five times without significant loss of activity and enantioselectivity.

Gold carbene chemistry from diazo compounds

Diazo compounds are generally used as carbene precursors. Traditionally, dirhodium, copper and iron catalysts were used to decompose diazo compounds to form the key metal carbene intermediates. Recently, the gold catalysts have been developed as a unique type of metal catalyst to decompose diazo compounds. The derived gold carbene showed much different characters comparing with other transition metal carbenes. They could go through a series of cycloaddition, insertion and coupling reactions. Here, the recent progress of the gold carbene chemistry from diazo compounds was reviewed, including the scope of reactions,mechanism and synthetic applications.

The cycloaddition reaction using visible light photoredox catalysis

In recent years, visible light photoredox catalysis has emerged as an important research area in synthesis. In this review, we describe the recent progress in the visible light induced cycloaddition reactions, including [2+2], [3+2], [4+2] and [2+2+2] cycloadditions, for the construction of four-, five- or six-membered cycles and polycycles. Furthermore, the mechanisms for these transformations are also discussed, in which the formation of the radicals is initiated by a visible light photoredox catalysis process.

Theoretical insights into the [4+2]/retro [4+2] cycloaddition approach to the synthesis of biaryls and polycyclic aromatics

A domino [4+2]/retro [4+2] cycloaddition process of cyclohexadienes with arylethynes or benzyne providing access to biaryls and polycyclic aromatics has been studied theoretically using density functional theory calculations. It has been found that the initial Diels-Alder (D-A) reaction acts as the rate-determining step and the consequent [4+2] cycloreversion reaction is feasible under the conditions used. Furthermore, the D-A reaction affects the regioselectivity, the origin of which is essentially derived from the good match of orbital coefficients between dienes and dienophiles as shown by using frontier molecular orbital (FMO) theory. Further investigation of the reactivity reveals that the reactions are predicted to fail to occur if an electron-donor group in the diene or an electron-acceptor group in the dienophile is lacking, as a consequence of the increased FMO energy gap. By further exploring the scope of substrates computationally, benzyne as an active dienophile was predicted to react with a variety of dienes in a cascade reaction under mild conditions with a low energy barrier, with the rate-determining step being the retro [4+2] cycloaddition.