亮点介绍

钯催化区域、非对映和对映选择性酰基硅的α位烯丙基烷基化反应及其在有机合成中的运用J.Am.Chem.Soc.2010,132,15493～15495钯催化的不对称烯丙基烷基化反应是非常高效的构建碳碳键方法     

过渡金属与光氧化还原协同催化的烯丙基取代反应的研究进展

过渡金属催化的烯丙基取代反应是一类重要且实用的有机化学反应, 可以立体选择性地高效构建碳-碳键和碳-杂键. 可见光氧化还原催化可以利用绿色清洁的可见光能源在较为温和的条件下产生自由基或者自由基离子等高反应活性的反应中间体, 被广泛地应用于有机合成中, 逐渐发展成为一种重要的合成工具. 鉴于烯丙基取代反应的重要性, 过渡金属与光氧化还原协同催化的烯丙基取代反应逐渐引起化学家的兴趣. 该协同催化的策略可以实现单一过渡金属催化难以实现的烯丙基取代反应, 反应的区域选择性和立体选择性也体现出不同的特点, 有望发展成为单一金属催化的烯丙基取代反应的重要补充. 本文综述了近年来不同过渡金属与可见光氧化还原协同催化的烯丙基取代反应的研究进展.     

钯卡宾参与的烯基芳烃轴手性化合物的合成

正Angew.Chem.Int.Ed.2016,55,2186~2190轴手性化合物因其具有独特的不可旋转的手性轴,在不对称催化等方面中有非常重要的应用.构建轴手性化合物最直接的方法之一是过渡金属催化的多组分的交叉偶联.中国科学技术大学顾振华课题组通过钯催化的溴代芳烃与腙化合物的偶联反应,以优异的产率得到了高对映选择性(ee约97%)的烯基芳烃轴手性化合物.反应通过芳基钯物种与卡宾形成钯卡宾中间体,最后迁移插入得到季碳钯物种,β-氢消除得到产物同时控制手性的产生.反应产率高,底物适用性好.产物可方便地转化为烯基膦配体(99%ee),并成功应用于不对称的烯丙基取代反应.     

二价钯催化的α或β联烯胺与烯丙基溴的偶联环化反应的研究

官能团化的联烯在过渡金属钯物种催化下的偶联环化反应作为一种有效的合成含氮、氧杂环的方法已经受到越来越多的重视[1].但是,联烯胺与烯丙基溴的偶联环化反应还没有被深入的研究过.我们组对钯催化下联烯醇与烯丙基溴的反应进行了一些研究[2],并基于此进行了联烯胺与烯丙基溴的偶联环化反应的研究.我们经过研究发现,可以通过二价钯催化,高效地经由α或β联烯胺与烯丙基溴的反应得到2,5-二氢吡咯或1,2,3,6-四氢吡啶类化合物,并且经过研究证明反应是通过二价钯的催化循环历程进行的.     

镍配合物催化的亚磷酸烯丙酯重排反应

烯丙基化合物在钯配合物催化下和亲核试剂的反应,已发展成为有机合成中的有用方法,我们曾在烯丙基化合物经钯催化的反应活性研究中,发现亚磷酸酯也是一个中等活性的离去基团;并发现在四(三苯膦)钯的催化下,亚磺酸烯丙酯能顺利地重排成相应的砜。但用四(三苯膦)钯为催化剂和亚磷酸烯丙酯反应时,不能分离得重排产物;进一步研究发现:在双(环辛二烯)镍的催化下,亚磷酸烯丙酯能够重排成相应的膦酸酯,反应温度要比相应的热重排低得多,而且时间短,产率高。     

醋酸锰(Ⅲ)催化2-(4-氨基苯基)苯并噻唑衍生物的合成研究

以取代的邻氨基硫酚为原料,三价醋酸锰催化条件下,与(取代)对硝基苯甲醛发生缩合反应,生成硝基苯并噻唑中间体,该合成工艺具有反应条件温和、操作简单等优点。在此基础上,利用钯碳催化还原反应,制备得到2-(4-氨基苯基)苯并噻唑化合物,总收率达到63-79%,利用IR、1HNMR和元素分析对目标化合物结构进行了表征。     

钯催化下稳定磷叶立德与烯丙基醇的脱水偶联反应

报道了钯催化下酮基稳定的磷叶立德与烯丙基醇一锅法的烯丙化-Wittig反应.研究表明,在5mol%四(三苯基膦)钯和20mol%硼酸的共催化下,以52%～95%的收率得到官能化1,4-二烯化合物.该方法还可以进一步拓展到酯基以及氰基稳定的磷叶立德来合成对应的1,4-二烯化合物.     

钯催化卤代芳烃Ullmann偶合反应

Ullmann偶合反应是有机合成中构建碳—碳键最重要的方法之一. 综述了钯催化卤代芳烃Ullmann偶合反应的研究进展, 其中包括钯催化还原Ullmann偶合反应和钯催化氧化Ullmann偶合反应等两部分.     

2,3-联烯醇及其衍生物的反应

2,3-联烯醇是一类含1,2-二烯官能团和羟基的化合物, 具有很高的反应活性, 它及其衍生物是一类重要的联烯化合物. 概述了2,3-联烯醇及其衍生物的反应, 包括2,3-联烯醇在过渡金属催化下的自身异构环化反应、钯催化的偶联反应、钌催化的环羰基化反应、不同条件下不同方式的扩环反应、亲电试剂参与的反应、分子内环加成反应、自由基反应等和2,3-联烯醇衍生物在零价钯催化下基于亚甲基-π-烯丙基钯中间体生成联烯或1,3-共轭二烯的区域选择性反应, S_N2'类型的加成-消除反应, 二价钯催化下的分子内环化反应以及重排反应等.     

钯催化烯丙基偕二醇二醋酸酯和各种亲核试剂的反应

研究了配体对烯丙基-1,1-偕二醇二醋酸酯(1)在钯配合物催化下和丙二酸酯钠盐反应的影响. 当用PPh3为配位体时, 丙二酸酯碳阴离子进攻在羰基碳上, 当用dppe为配体时, 进攻在烯丙基碳上. 亲核试剂的性质也影响反应进攻的位置. 通过选择适当的亲核试剂和配体可以从1得到二次烷基化的产物.     

CO2在铜电极上的电还原行为

对常温常压下的MeCN, DMF和DMSO等3种有机溶剂中的CO2的电还原反应行为进行了研究, 求得了传递系数和扩散系数, 并证明了在MeCN, DMF和DMSO中, CO2的还原反应是受扩散控制的不可逆过程.     

Electrochemical reduction of camphorquinone in DMF in the presence of a proton donor

The electroreduction of camphorquinone in DMF, at mercury electrodes, was investigated by a variety of techniques. In DMF, in the absence of proton donor, camphorquinone exhibits two one-electron waves: the first, a one-electron reversible wave to be due to a reversible charge transfer without a coupled chemical reaction. After the first charge transfer, the semidione anion radical is reduced to the dianion. The irreversibility of the second wave derives from a fast irreversible protonation of the dianion. A wide variety of changes in behaviour is observed in the reduction of camphorquinone as increasing amounts of benzoic acid are added: a new two-electron irreversible wave appears at a potential less negative than the original wave. A proton donor to substrate ratio of 2 is required to completely suppress the two original waves. A mechanism for the electroreduction of camphorquinone is proposed and discussed on the basis that the prewave current is controlled by the diffusion of the undissociated acid species and that the undissociated acid, rather than the solvated proton, takes part in the protonation, prior to the charge transfer.     

An electrochemical study of (η-C5H5)2Ti(NCS)2

The reduction of titanocene dithiocyanate in various solvents has been examined using the techniques of polarography, voltammetry, controlled potential electrolysis and cyclic voltammetry. In THF and CH₂Cl₂, Cp₂Ti(NCS)₂ undergoes successive one-electron transfer reactions, and by using a combination of electrochemical and EPR techniques it has been possible to confirm the stability of [Cp₂Ti(NCS)₂]^? in these solvents. In DMF, however, an irreversible dimerization follows the first electron transfer.     

Evidence for the formation of a cationic surface layer on silver,copper and gold under potential cycling conditions: a possible interpretation of the electro-magnetic field effect involved in sers phenomena

The electrode reduction mechanism of benzenedicarbonitrile isomers has been investigated in DMF, in different protogenic conditions, by polarography, cyclic voltammetry and controlled potential electrolysis. Radical anions produced by quasi-reversible one-electron transfer undergo CCN bond breaking only through preliminary proton transfer, the kinetic basicities of the radicals depending upon their structure. For the 1,2- and 1,4-isomers, two-electron reduction yields the corresponding dianions, which also undergo CCN bond breaking via proton transfer, the latter mainly taking place in the double-layer region or in the bulk, according to the experimental conditions.     

酞菁锌高效催化以二氧化碳、含氢硅烷和有机胺为原料合成甲酰胺类衍生物

目前为了有效地利用好CO2,主要策略有以下几种:(1)"水平途径"——无价态及能量变化,譬如生成尿素、环状碳酸酯、聚碳酸酯及噁唑烷酮类衍生物等;(2)"垂直途径"——有价态及能量变化,譬如直接加氢转化成碳一产品(甲酸、甲醛、甲醇、甲烷)等;(3)"对角线途径"——有价态及能量变化,即结合石油化工原料将CO2还原生成醇、醚、羧酸、亚胺、酰胺、酯等系列高附加值的精细有机化工产品.其中以二氧化碳和含氢硅烷为原料,通过有机胺的N-甲酰化反应合成甲酰胺类衍生物符合绿色化学和可持续发展的要求.基于仿生催化CO2分子活化的基本理论,我们借鉴强极性的有机溶剂可有效活化硅氢键的性质,创新性地将廉价易得的酞菁锌(ZnPc)作为类酶催化剂,并以化学计量的N,N'-二甲基甲酰胺(DMF)为添加剂,构成组分新颖并高效绿色的类酶协同催化体系,实现了在温和反应条件下高效高选择性地合成甲酰胺类衍生物.研究发现:以苯硅烷作为还原剂,当加入0.5 mol%ZnPc和2 mmol DMF,在25℃和0.5 MPa下仅需反应6 h,可得到收率为99%的N-甲基甲酰苯胺.更值得注意的是,当以更易得的聚甲基氢硅烷(PMHS)为还原剂时,加入5 mol%ZnPc和1 mL DMF,在80℃和1 MPa下反应8 h,N-甲基甲酰苯胺的收率也高达99%.实验结果表明:添加剂DMF可以通过溶剂化和强极性作用高效活化含氢硅烷中的Si?H键,然后具有亲电性的金属活性中心能够稳定氢负离子生成高活性锌氢中间体.即ZnPc/DMF之间的协同催化作用能够促进氢化物从含氢硅烷转移到CO2分子,进而有利于CO2分子的高效活化.综上所述,利用类酶催化剂反应专一性的特点,通过有机胺的N-甲酰化反应,实现了以CO2和含氢硅烷为原料在温和条件下甲酰胺类衍生物的绿色高效合成.这对于设计和开发更加高效的催化体系具有一定的指导作用和借鉴意义.     

Electrochemical behavior of C-(60) modified electrode in aqueous solutions

The construction of adsorptive type C60 modified electrode and its electrochemical reduction and oxidation behavior in aqueous solutions are described in this report. Four pairs of one-electron transfer reduction and oxidation cyclic voltammetry is obtained in aqueous solution containing 30% CH3CN and 2% (C2H5)4NOH. It is reported in this paper that the C60 modified electrode also catalyzes the electrochemical reduction of dissolved oxygen in 40% DMF and 2% (C2H5)4NOH aqueous solution and this might open a new field for the potential applications of C60 in electrochemistry and electroaualytical chemistry.     

Superior dispersion of highly reduced graphene oxide in N,N-dimethylformamide

Here, we report the effect of temperature on the extent of hydrazine reduction of graphene oxide in N,N-dimethylformamide (DMF)/water (80/20 v/v) and the dispersibility of the resultant graphene in DMF. The highly reduced graphene oxide (HRG) had a high C/O ratio and good dispersibility in DMF. The good dispersibility of HRGs is due to the solvation effect of DMF on graphene sheets during the hydrazine reduction, which diminishes the formation of irreversible graphene sheet aggregates. The dispersibility of the HRGs was varied from 1.66 to 0.38 mg/mL when the reduction temperature increased from 25 °C to 80 °C. The dispersibility of the HRGs was inversely proportional to the electrical conductivity of the HRGs, which varied from 17,400 to 25,500 S/m. The relationships between the C/O ratio, electrical conductivity, and dispersibility of the HRGs were determined and these properties were found to be easily controlled by manipulating the reduction temperature.     

Macromlecular engineering of polylactones and polylactides. XVI. On the way to the synthesis of ω-aliphatic primary amine poly (ϵ-caprolactone) and polylactides

Since bromides are well-known precursors of primary amines, diethylaluminum 12 bromo-1-dodecyl oxide has been prepared and used as an initiator for the ring-opening polymerization of ?-caprolactone and L-lactide. Uner strictly controlled conditions, the end-functionalization of the polyesters in quantitative and the bromo end-group is easily converted into an azide group whatever the polymeric backbone. The subsequent reduction of the azide into the expected primary amine has been investigated by catalytic transfer hydrogenation (CTH) in DMF and by hydrolysis in the presence of triphenylphosphine in THF, respectively.The hydrolysis reaction (PΦ₃/H₂O) is perturbed by a coupling reaction, which involves a protonate secondary amine and leads to a twofold increase in the polyester molecular weight. The CTH method gives rise to the expected ω-NH₂ poly (?-caprolactone), in contrast to polylactide which seems to be unstable toward the nascent amine end group. Whatever the polarity of the medium (DMF or THF), aminolysis of polylactides is observed to occur and leads to the formation of an internal amide. © 1994 John Wiley & Sons, Inc.     

Chain transfer to solvent in the radical polymerization of N‐isopropylacrylamide

Chain transfer to solvent has been investigated in the conventional radical polymerization and nitroxide‐mediated radical polymerization (NMP) of N‐isopropylacrylamide (NIPAM) in N,N‐dimethylformamide (DMF) at 120 °C. The extent of chain transfer to DMF can significantly impact the maximum attainable molecular weight in both systems. Based on a theoretical treatment, it has been shown that the same value of chain transfer to solvent constant, C_tr,S, in DMF at 120 °C (within experimental error) can account for experimental molecular weight data for both conventional radical polymerization and NMP under conditions where chain transfer to solvent is a significant end‐forming event. In NMP (and other controlled/living radical polymerization systems), chain transfer to solvent is manifested as the number‐average molecular weight (M_n) going through a maximum value with increasing monomer conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Electrochemically controlled hydrogen bonding. Redox-dependent formation of a 2:1 diarylurea/dinitrobenzene2- complex

[reaction: see text] The electrochemistry of 1,2-dinitrobenzene (1,2-DNB), 1,3-dinitrobenzene (1,3-DNB), and 1,4-dinitrobenzene (1,4-DNB) is strongly affected by the presence of 1,3-diphenylurea. In DMF, the second reduction potential of all three DNBs shifts substantially positive in the presence of the urea, indicating very strong hydrogen bonding to the dianions. With 1,2- and 1,3-DNB, the hydrogen bonding leads to irreversible chemistry, likely due to proton transfer from the urea to the dianions. No such irreversible behavior is observed with 1,4-DNB. Instead, the second reduction shifts into the first reduction, producing a single, reversible, two-electron cyclic voltammetric wave at high urea concentrations. Computer simulations show that the changes in wave shape accompanying this process are well accounted for by the stepwise formation of a 1:1 and 2:1 1,3-diphenylurea/DNB2- complex, with sequential binding constants of approximately 5.5 x 10(4) M(-1) and approximately 4.0 x 10(3) M(-1) in DMF.