离子液体在有机合成中的应用研究进展

离子液体由于具有特殊的性质, 包括低挥发性、大极性、良好的热稳定性、通过调整阴阳离子选择不同的溶解性等特点, 已经作为反应介质或催化剂广泛应用于有机合成领域, 引起了人们足够的兴趣. 与传统有机溶剂反应相比, 离子液体相反应得到的产物收率高, 选择性好, 加快部分类型反应的速率, 后处理简单以及离子液体催化剂体系简单, 回收后, 可多次重复使用. 综述了离子液体作为反应介质或催化剂在有机合成传统反应类型中的最新研究成果, 主要包括: 偶联反应、Michael加成、Baylis-Hillman反应、Diels-Alder反应、Aldol缩合、Knoevenagel缩合、环化反应、烷基化及酰基化反应和氧化还原反应.     

微波促进离子液体相反应在有机合成中的应用

微波促进离子液体相有机合成技术作为一种新型的绿色化学合成法,引起了人们极大的兴趣。在离子液体中,微波辅助下反应快速、收率高、选择性好、后处理简单,离子液体经简单再生后可多次套用。本文综述了以离子液体为反应介质或催化剂的微波辅助技术在多种类型有机反应中的研究成果,主要包括了环合反应、亲核取代反应、金属复分解反应、酰化反应、重排反应、聚合反应、偶联反应、氧化还原反应和选择性脱溴反应等。     

The Effect of Position Replacement of Functional Groups on the Stepwise character of 1,3‐Dipolar Reaction of a Nitrile Oxide and an Alkene

It is a well‐known fact that by changing the 1,3‐dipolar cycloaddition (1,3‐DC) reaction mechanism from concerted to stepwise, the stereospecificity is lost; since in synthesizing the required heterocyclic molecules that reaction is a requisite, it is important to study the concertedness of that reaction. Several papers on this subject have already stated that the existence of electron withdrawing groups (EWG) or electron donor groups (EDG) on dipole or dipolarophile leads to a high‐energy differentiation between the dipole HOMO and dipolarophile LUMO (or vice versa) as well as the emergence of an intermediate in the reaction pathway. This paper seeks answering the question of when an EWG on dipole and an EDG on dipolarophile could be a factor in making the reaction mechanism stepwise, and does repositioning of functional groups in replacing dipole and dipolarophile switches the reaction mechanism from stepwise into concerted or vice versa?     

New approaches to heck reaction testing for homogeneity-heterogeneity

Modified catalytic reaction tests for homogeneity-heterogeneity are proposed. In these tests, the time dependence of a reaction response (conversion, product yield, or selectivity) to various manipulations used in traditional tests rather than the suppression or retention of catalytic activity (positive or negative test results) is of crucial importance. With the use of the Heck reaction as an example, it is demonstrated that the results of these modified and traditional tests can lead to opposing conclusions. In this case, the results of the modified tests are consistent with each other and with the results of studies on the kinetics and selectivity of the reaction, as well as with a great body of other experimental data published in the past five to seven years, which are indicative of the true homogeneous character of the Heck reaction.     

氟喹诺酮作为钯催化Heck反应有效配体的研究

研究了氟喹诺酮作为钯催化Heck反应的有效配体. 碘苯、溴苯和其它芳基卤衍生物与丙烯酸丁酯、苯乙烯等取代乙烯类化合物在钯和氟喹诺酮的催化下发生Heck反应. 讨论了配体、催化剂用量、碱和溶剂对Heck反应产率的影响. 该反应的最优化条件是: 钯源为Pd(OAc)2 (0.1 mol%), 诺氟沙星作为配体(0.2 mol%), K2CO3作为碱, DMA作为溶剂, 取代碘苯及溴苯和它们的衍生物与丙烯酸丁酯、苯乙烯等乙烯基化合物的反应均可以得到高收率的目标偶联产物.     

三甲基硅化腈在有机合成中的应用

三甲基硅化腈是一种常用的有机合成试剂. 对近年来三甲基硅化腈在有机合成中的应用进行了简要的总结和概述, 重点介绍了三甲基硅化腈作为强的亲核试剂广泛用于环氮和环氧化合物的开环反应、亚胺和醛酮类化合物的加成、胺与醛或酮参与的多组分反应、偶联反应以及对炔和具有较高活性的碳碳双键的氰化加成等反应.     

THE CHLOROPHYLL-SENSITIZED REACTION BETWEEN BENZOQUINONE AND ETHANOL*

The electron-transfer reaction between triplet excited chlorophyll and quinones has been extensively studied as a model of the primary reaction in photosystem II. There has also been reported a minor reaction in which the chlorophyll cation radical ostensibly oxidizes the alcohol solvent or even water, leading to a gradual net reduction of quinone, but the exact mechanism and even the existence of this reaction has been uncertain. We have examined the consequences of prolonged irradation of ethyl chlorophyllide and benzoquinone in acidulated ethanol, and find a chlorophyllide-sensitized reaction which is not analogous to the better-known autosensitized reduction of quinones in blue or UV light. In the chlorophyllide-sensitized reaction, benzoquinone is apparently converted to ethoxy-substituted quinones and quinols, and polymeric material. Ethyl chlorophyllide (or chlorophyll) is simultaneously oxidized to more polar products which themselves continue to photosensitize the reaction of quinones. The production of acetaldehyde could not be demonstrated in the sensitized reaction. Chlorophyllide-sensitized reaction of (l-hydroxyethyl)benzoquinone, ethoxybenzoquinone and 2.5-diethoxybenzo-quinone were examined for additional information. A reaction sequence, tentatively proposed to accommodate the known facts, starts with oxidative attack by quinone on an oxidized chlorophyllide radical formed by loss of a hydroxyl proton from alcohol bound as a ligand to Mg²⁺. It is not likely that this reaction is closely related to events at the oxidizing side of photosystem II.     

迈克尔反应受体分子化学生物学研究

迈克尔受体是烯键或炔键与吸电子基团共轭相连形成的官能团,含有这样官能团的化学小分子能与亲核试剂发生迈克尔加成反应,因此称为迈克尔反应受体分子。迈克尔反应受体分子是一类重要的生理活性分子,它们直接或间接参与许多生命过程,同时也是细胞中许多信号转导途径的调节者,在化学生物学研究中起着重要的作用。本文对迈克尔反应受体分子化学生物学研究进展进行了综述。     

Pyrrolidine and α-methylene-α-lactam from the cyclization of α-(alkylaminoethyl)acrylate: Synthesis of aza-sarkomycins

Diene readily adds primary amines to give which can cyclize either in a Michael addition fashion or via a displacement reaction to give, respectively, pyrrolidine or methylene lactam which further isomerizes to under the employed reaction conditions. Compound can be obtained as the sole product from the reaction of diene precursor with amines followed by vacuum pyrolysis.     

Microwave Heating Outperforms Conventional Heating for a Thermal Reaction that Produces a Thermally Labile Product: Observations Consistent with Selective Microwave Heating

Microwave (MW) heating is more effective than conventional (CONV) heating for promoting a high‐temperature oxidative cycloisomerization reaction that was previously reported as a key step in a total synthesis of the natural product illudinine. The thermal reaction pathway as envisioned is an inverse electron‐demand dehydro‐Diels–Alder reaction with in situ oxidation to generate a substituted isoquinoline, which itself is unstable to the reaction conditions. Observed reaction yields were higher at a measured bulk temperature of 200 °C than at 180 °C or 220 °C; at 24 hours than at earlier or later time points; and when the reaction solution was heated using MW energy as opposed to CONV heating with a metal heat block. Selective MW heating of polar solute aggregates is postulated to explain these observations.     

Time behaviour of the modifier involved in the general mechanism of Botts and Morales assuming rapid equilibrium in the modifier bindings

To date, the classification as activator or inhibitor of a modifier involved in an enzyme catalysed reaction is established according to its kinetic behaviour at the steady state. Inhibitors and activators are defined as modifiers which decrease or increase, respectively, the steady state rate of an enzyme-catalysed reaction. At this state, in some cases, a modifier always acts as an activator or as an inhibitor for all its possible concentration values. In other cases the action of a modifier as activator or inhibitor depends on its concentration. In this paper we extend the analysis of the kinetic behaviour of a modifier as inhibitor or nonessential activator to the transient phase of the reaction, i.e. to the whole course of the reaction, including both the transient phase and the steady state. Moreover, concerning to the behaviour of a modifier at the transient phase, we suggest its classification as activator or inhibitor based on the concentration and activator or inhibitor based on the rate. We have studied the behaviour of the modifier involved in the general modifier mechanisms of Botts and Morales in which the reversible bindings of the modifier to the enzyme forms are assumed in rapid equilibrium. The result is that depending on the values of the rate constants, equilibrium constants and the initial concentrations of both the involved substrate and modifier, the latter can act during the whole reaction course only as an activator, only as an inhibitor, first as an activator and then, from a determined reaction time, as inhibitor, or vice versa. Therefore, it is possible that a modifier showing an activating behaviour at the steady state behaves as an inhibitor in the transient phase, or vice versa. Novel indices pointing to the conditions under which the modifier can show any of the behaviours indicated above are suggested. The goodness of the analytical results is tested by comparison with the simulated curves obtained by numerical integration. From these results, those corresponding to several reaction mechanisms involving a modifier, and which can be regarded as particular cases of the general case analysed here, can be directly and easily obtained.     

Synthesis of polyhydroxylated bicyclic tetrahydrofurans and tetrahydropyrans via a stereoselective domino cyclization/reduction reaction

A novel reaction cascade involving a Lewis acid-induced migration of an isopropylidene protecting group followed by the formation of a pyranose or furanose ring and subsequent reduction of the hemiacetal is described. Depending on the reaction conditions, as well as, the stereochemistry of the substrate, polyhydroxylated tetrahydrofurans or tetrahydropyrans can be obtained in reasonable yields. The synthons used in this transformation were prepared via a highly stereoselective one-pot tandem reaction, consisting of a 1,4-Michael addition of vinylmagnesium bromide to d-glucose-derived cyclohexenone followed by aldol reaction with 2,3-O-isopropylidene-d-glyceraldehyde.     

Zn-promoted regioselective and sequence-selective one-pot joining reaction of three components: alkyl iodides, alpha,beta-unsaturated esters (or nitriles), and acylating agents

One-pot treatment of alkyl iodides, alpha,beta-unsaturated esters (or nitriles), and acylating agents such as nitriles or acid anhydrides in the presence of Zn metal at room temperature in the same reaction system brought about a regioselective and sequence-selective three-component joining reaction involving first C-alkylation at the beta-position and second C-acylation at the alpha-position of alpha,beta-unsaturated esters (or nitriles) to afford the corresponding alpha,alpha-dialkylketoesters (or alpha,alpha-dialkylketonitriles) in moderate to good yields. [reaction: see text]     

Poly(vinyl chloride) stabilization with organo-tin compounds: Part VII—Dibutyl tin maleate: Model compound studies

The reaction between dibutyl tin maleate or dibutyl tin bisbutylmaleate and chlorohexene as a model compound for allylic chloride in PVC was studied at 80°C in dichlorobutane solution. From kinetic studies by gas chromatographic analysis of the reaction medium, and also spectroscopic data (infra-red and ¹H NMR) it may be concluded that the main reaction is the substitution reaction which produces mono- and dihexenyl esters, as well as mixed diesters of maleic acid. The elimination reaction plays a minor rôle. Both activities are related to their Lewis acidities. The Diels-Alder condensation between maleates and hexadiene is not observed as a side reaction in these conditions; the main side reaction is the decomposition of monoesters of maleic acid (which is produced by the elimination reaction after one or two steps) into an alcohol and maleic anhydride—a reaction which can be catalysed by organo-tin chlorides. A Diels-Alder reaction between maleic anhydride and hexadiene takes place. The alcohol produced in the side reaction mentioned above may take part in a transesterification reaction with the organo-tin maleate and that reaction probably provides the best explanation of the earlier observation of Frye et al.,¹ according to which there is at least temporary retention of reactivity of tin labelled organo-tin maleate by PVC.     

The thiazolium-catalyzed Sila-Stetter reaction: conjugate addition of acylsilanes to unsaturated esters and ketones

A new acyl anion addition reaction between acylsilanes and alpha,beta-unsaturated conjugate acceptors promoted by a nucleophilic organic catalyst has been disclosed. The 1,4-dicarbonyl products produced in this reaction are highly useful synthons. Neutral carbenes (or zwitterions) generated in situ from commercial thiazolium salts are used as effective catalysts for the reaction which is in contrast to established anionic catalysts typically employed to promote the required Brook rearrangement (1,2-silyl shift from carbon to oxygen) involved in the reported reaction. This process successfully utilizes acylsilanes as tunable acyl anion progenitors and is tolerant of a wide range of structural diversity on the acylsilane or the conjugate acceptor.     

Review of Acetic Acid Synthesis from Various Feedstocks Through Different Catalytic Processes

Acetic acid (AA) has been largely used with a wide range of applications such as a raw material for a synthesis of vinyl acetate monomer, cellulose acetate or acetate anhydrate, acetate ester and a solvent for a synthesis of terephthalic acid and so on. The present paper briefly summarizes the commercialized chemical processes with their Rh or Ir-based catalytic systems in a liquid-phase carbonylation reaction such as Monsanto, Cativa and Acetica processes. In addition, some alternative catalytic systems such as heterogeneous catalysts to produce AA by direct oxidation or indirect carbonylation of dimethyl ether through BP-SaaBre process in a gas-phase reaction to solve some problems such as a difficult separation of homogeneous catalysts in a corrosive reaction medium. Some home-made heterogeneous catalysts such as a rhodium incorporated graphitic carbon nitride (Rh-g-C₃N₄) and some heterogenized homogeneous catalysts using the supports of tungsten carbide, iron oxide or graphitic carbon nitride containing rhodium complexes were also introduced for the synthesis of AA through a liquid-phase methanol carbonylation reaction to effectively solve the leaching problem of active rhodium metal as well as to mitigate the separation problem of homogeneous catalysts.     

Cuprous Iodide Catalyzed Synthesis of Diaryl Selenide and Telluride from Organoboronic Acids with Diphenyl Diselenide and Ditelluride

Organoselenium and tellurium compounds have received much attention not only as synthetic reagents or intermediates in organic synthesis but also as promising donor molecules for conductive materials.[1] A number of synthetic methods have been reported to prepare organoselenium and tellurium derivatives. A convenient and general method to introduce a selenium or tellurium moiety into organic molecules is the reaction of a metal selenolate or tellurolate with appropriate electrophiles such as organic halides, acyl chlorides, epoxides, and α, β-enones.[2] However, it is difficult to synthesize the unsymmetrical diarylselenides and tellurides through the reaction of selenide anion with organic halides because of the less reactivity of aryl halides. To accomplish this purpose, the reaction (iodobenzene with phenylselenol)was generally carried out in the presence of catalysts, ligands and strong bases. But, the reaction needs longer time to accomplish and form the products in moderate yields.     

Product distribution in preparative scale electrolysis: Part I. Introduction

The purpose of the present series is to establish and discuss the relationships between the distribution of products in preparative scale electrolysis and characteristic rates or ratios and magnitude of the operational parameters for a set of reaction schemes that can be encountered in a large variety of electrochemical processes. This can help in optimizing the yield of the target product for a given electrosynthetic reaction by a proper choice of the reaction conditions. Furthermore, systematic analysis of the product distribution as a function of the various parameters may in many cases be the only route to the reaction mechanism due to the time-scale limitations of the standard electrochemical kinetic techniques. The reaction sequences thus considered involve, besids electron transfer at the electrode, fast accompanying chemical reactions and competing chemical or electrochemical follow-up reactions. Reaction intermediates are thus confined within a reaction layer the thickness of which is small as compared to that of the diffusion layer in the context of the Nernst approximation. The other basic assumptions and procedures of resolution of the mathematical models are defined and discussed. Three different electrolysis regimes are considered involving potentiostatic or galvanostatic control and continuous or discontinuous electrolysis operations. A first reaction scheme is analyzed within this context involving the competition between homogeneous and heterogeneous electron transfer after a first electron transfer followed by an irreversible chemical step. The preliminary resolution of this ECE-Disp problem is indeed required for a number of reaction mechanisms of more definite chemical interest.     

Asymmetric multicomponent reactions (AMCRs): the new frontier

Asymmetric multicomponent reactions involve the preparation of chiral compounds by the reaction of three or more reagents added simultaneously. This kind of addition and reaction has some advantages over classic divergent reaction strategies, such as lower costs, time, and energy, as well as environmentally friendlier aspects. All these advantages, together with the high level of stereoselectivity attained in some of these reactions, will force chemists in industry as in academia to adopt this new strategy of synthesis, or at least to consider it as a viable option. The positive aspects as well as the drawbacks of this strategy are discussed in this Review.