共查询到20条相似文献,搜索用时 78 毫秒
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新颖的纳米镍催化芳基硼酸与芳基溴的偶联反应 总被引:7,自引:0,他引:7
纳米镍用于催化芳基硼酸与芳基溴的偶联反应,合成了一系列4,4′-双烷基环己基联苯类液晶,纳米镍在相转移剂十六烷基三甲基溴化铵的存在下回流反应15h,目的产物的收率为60%-65%。讨论了纳米镍催化偶联反应的可能活性位,镍催化剂经SEM-EDS表征平衡粒径为80nm,定量分析表明氧含量为33%;XRD测试结果表明纳米镍体相以单质态存在,但其特征谱线的d值普遍增大;由XPS分析得聘书纳米镍的结合能(2p3/2和2p1/2)为854.1eV和871.8eV,峰间距为17.7eV,表明纳米镍是以介于单质镍和氧化镍之间的价态存在。 相似文献
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Maestri G Motti E Della Ca' N Malacria M Derat E Catellani M 《Journal of the American Chemical Society》2011,133(22):8574-8585
Mechanistic questions concerning palladium and norbornene catalyzed aryl-aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the "ortho effect" (caused by an ortho substituent in the starting aryl halide), which leads to aryl-aryl coupling with a second molecule of aryl halide rather than to aryl-norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading to Pd(IV). The unselective sp(2)-sp(2) and sp(2)-sp(3) coupling, experimentally observed in this case, can be explained in the framework of the transmetalation pathway since the energetic difference between aryl attack onto the aryl or norbornyl carbon of the palladacycle intermediate is quite small. On the other hand, according to the experimentally observed "ortho effect", selective aryl-aryl coupling only occurs in the reactions of ortho-substituted metallacycles. The present work offers the first possible rationalization of this finding. These in situ formed palladacycles containing an ortho substituent could more easily undergo oxidative addition of an aryl halide rather than reductive elimination from the transmetalation intermediate as a result of a steric clash in the transition state of the latter. The now energetically accessible Pd(IV) intermediate, featuring a Y-distorted trigonal bipyramidal structure, can account for the reported selective aryl-aryl coupling through a reductive elimination which is easier than aryl-norbornyl coupling. Thus, the steric effect represents the main factor that dictates the energetic convenience of the system to follow the Pd(IV) or the transmetalation pathway. Ortho substituents cause a higher energy transition state for reductive elimination from the transmetalation intermediate than for oxidative addition to the metallacycle palladium(II) and the pathway based on the latter predominates. 相似文献
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We synthesize four- and six-member cyclic products via sequential multi-step aryl-aryl coupling reactions of 2,3,6,7,10,11-hexabromotriphenylene molecules on a Au(111) surface. The final products as well as the organo-gold intermediate structures are identified using scanning tunneling microscopy and density-functional theory simulation. By adjusting reaction temperature and post-annealing temperature, we enhance/suppress the yields of the four-member and six-member cyclic products. We propose an underlying mechanism which is associated with different reaction kinetics of the first-order and second-order reactions. This work exemplifies intricate kinetically-controlled on-surface synthesis when multiple reactions of different reaction order are involved. 相似文献
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Amit Kumar 《Tetrahedron letters》2007,48(41):7283-7286
A regioselective synthesis of unsymmetrical biaryls with electron withdrawing or donating substituents is described and illustrated by carbanion-induced ring transformation of 6-aryl-α-pyrones with methoxyacetone in excellent yield. Our methodology is an alternative to classical organometal-catalyzed aryl-aryl coupling reactions and can be applied to the synthesis of functionally demanding naphthyl biaryls for the development of new ligands for asymmetric synthesis. 相似文献
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Rajeshwar Reddy Aleti Alexey A. Festa Leonid G. Voskressensky Erik V. Van der Eycken 《Molecules (Basel, Switzerland)》2021,26(18)
Phenanthridinones are important heterocyclic frameworks present in a variety of complex natural products, pharmaceuticals and displaying wide range of pharmacological actions. Its structural importance has evoked a great deal of interest in the domains of organic synthesis and medicinal chemistry to develop new synthetic methodologies, as well as novel compounds of pharmaceutical interest. This review focuses on the synthesis of phenanthridinone scaffolds by employing aryl-aryl, N-aryl, and biaryl coupling reactions, decarboxylative amidations, and photocatalyzed reactions. 相似文献
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Development of synthetic methods for silole-containing or –fused polycyclic aromatic compounds has been in great demand. Described in this paper is an easy synthetic method for the high-efficient synthesis of chrysenosilole derivatives from silatricyclic compounds via the Mallory photocyclization reaction. It is noteworthy that those conventional transition-metal and Lewis acid catalyzed or mediated CC bond coupling reactions did not work well for this aryl-aryl coupling reaction. 相似文献
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tert-Butyl phenylazocarboxylates are versatile building blocks for synthetic organic chemistry. Nucleophilic substitutions of the benzene ring proceed with aromatic amines and alcohols under mild conditions. The attack of aliphatic amines may be directed to the aromatic core as well as to the carbonyl unit leading to azocarboxamides. The benzene ring can further be modified through radical reactions, in which the tert-butyloxycarbonylazo group enables the generation of aryl radicals at either elevated temperatures or under acidic conditions. Radical reactions include oxygenation, halogenation, carbohalogenation, carbohydroxylation, and aryl-aryl coupling. 相似文献
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L Chausset-Boissarie R Àrvai GR Cumming L Guénée EP Kündig 《Organic & biomolecular chemistry》2012,10(32):6473-6479
The total syntheses of the Lythracea alkaloids (+)-vertine and (+)-lythrine are described. Enantioenriched pelletierine is used as a chiral building block and engaged into a two step pelletierine condensation leading to two quinolizidin-2-one diastereomers in a 8 : 1 ratio. The major product is used in the synthesis of (+)-vertine via aryl-aryl coupling and ring closing metathesis to provide a Z-alkene α to the lactone carbonyl function. The same procedure was used for (+)-lythrine after base induced epimerization of the main quinolizidin-2-one diastereomer. Alternative classical ring closure strategies like macrolactonisation or aryl-aryl coupling failed. 相似文献
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Petra Walter Dr. Olaf Hübner Dr. Elisabeth Kaifer Prof. Hans-Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(46):11943-11956
Proton-coupled electron transfer (PCET) is of key importance in modern synthetic chemistry. Redox-active guanidines were established by our group as valuable alternatives to toxic high-potential benzoquinones in a variety of different PCET reactions. In this work, the PCET reactivity of a series of 1,4-bisguanidino-benzenes varying in their redox potentials and proton affinities is evaluated. The relevant redox and protonation states are fully characterized, and the compounds sorted with respect to their PCET reactivity by comparative PCET experiments supplemented by quantum-chemical calculations. Depending on the studied reactions, the driving force is either electron transfer or proton transfer; thereby the influence of both processes on the overall reactivity could be assessed. Then, two of the PCET reagents are applied in representative oxidative aryl-aryl coupling reactions, namely the intramolecular coupling of 3,3’’-4,4’’-tetramethoxy-o-terphenyl to give the corresponding triphenylene, the intermolecular coupling of N-ethylcarbazole to give N,N’-diethyl-3,3’-bicarbazole, and in the oxidative lactonization of 2-[(4-methoxyphenyl)methyl]-benzoic acid. Under mild conditions, the reactions proceed fast and efficient. Only small amounts of acid are needed, in clear contrast to the corresponding coupling reactions with traditional high-potential benzoquinones such as DDQ or chloranil requiring a large excess of a strong acid. 相似文献
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研究了以Pd(OAc)2为催化剂,H3PMo12O40为助催化剂,空气为氧化剂,在乙酸溶液中于373 K条件下,在500 ml高压釜中由苯液相氧化偶联合成联苯. 结果表明,反应产物中联苯的选择性高达92%以上,并且只有少量的三联苯副产物生成. 分别考察了H3PMo12O40的加入量和O2分压对以空气或纯O2为氧化剂时Pd/HPMo/AcOH催化苯液相氧化偶联合成联苯反应催化性能的影响. 根据反应液颜色的变化以及文献结果推测,在反应过程中通过钯和钼物种的氧化和还原作用使苯氧化生成联苯. 相似文献