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.     

基于Heck插入策略的钯催化烯烃与α-溴代烷基羰基化合物的烯烃氧化双官能化反应合成吲哚2-酮类化合物

正钯催化Heck偶联反应一般首先经过插入和加成步骤生成含C—Pd键中间体A,最后通过β-H消除来实现钯催化循环.如何利用中间体A中的C—Pd键引入新官能团是有机合成研究难点之一.目前有两种策略:(1)零价钯催化体系下,烯烃与卤代烃反应生成含C—Pd键中间体A,然后与亲核试剂(芳基硼酸,Cl-,CO,烯烃和炔烃等)实现烯烃双官能团化反应;(2)两价钯/氧化剂催化体系下,烯烃与有机金属试剂反应生成含C—Pd键中间体A,然后与亲核试     

零价钯和苯甲酸共催化内炔烃氢胺化反应机理的理论研究

通过密度泛函方法(DFT)研究了零价钯和苯甲酸共催化内炔烃氢胺化反应的机理.计算研究表明,文献中推测的通过苯甲酸的O—H键氧化加成到零价钯上形成钯氢中间体并不是启动该反应的有利途径.机理如下:在零价钯炔烃复合物上,苯甲酸可以通过质子转移到炔烃的途径得到二价烯基钯中间体,生成的羧酸根阴离子可以进一步辅助底物发生β-氢消除反应生成联烯中间体,随后在零价钯联烯复合物上,再次通过苯甲酸质子转移得到烯丙基钯中间体,最后胺亲核进攻烯丙基末端碳得到最终氢胺化产物.     

钯催化下芳基磺酸酯和芳基硅烷的Hiyama交叉偶联反应

钯催化下有机硅试剂和有机亲电试剂的Hiyama偶联反应是形成碳-碳键的重要方法之一．相较于有机锌、锡试剂和格氏试剂,有机硅试剂易于操作,对空气和水也较稳定,且毒性很低．另一方面,芳基磺酸酯作为交叉偶联反应中的亲电试剂正在受到很大关注．作为酚的衍生物,此类化合物廉价易得,性质稳定且易于操作．     

钯催化下有机锡化合物的偶联反应在碳-碳键形成过程中的应用

本文述评了最近几年来钯催化的有机锡化合物与有机亲电试剂的交叉偶联反应在有机合成中用于碳-碳键形成的主要研究成果。主要讨论了直接交叉偶联反应,CO或烯键插入的交叉偶联反应和机理。     

钯催化Stille交叉偶联反应研究新进展

综述了钯催化Stille交叉偶联反应的最新研究进展, 主要包括三个方面: (1)有机锡化合物与有机亲电试剂如卤代芳香烃、卤代烷烃、酰氯等的反应; (2)Stille反应的机理; (3) Stille反应在有机合成中的应用.     

钯(II)配合物和氯化锌在DMF中阴极还原的动力学

烯丙基化合物在钯催化下与碳亲核试剂的反应已成为碳一碳键合成的手段.1989年王志勤等研究报导,在DMF溶液中和氯化锌存在下,钯催化醋酸烯丙酯与羰基化合物电化学还原生成高产率的醇.我们对此反应的机理进行了研究,首先用线性电势扫描法确定各电还原反应的还原电势,得出在实验条件下,氯化锌比π-烯丙基钯配合物容易还原,然后     

可见光诱导的钯催化Heck反应

Heck反应作为构建C—C键最为强大和实用的合成工具之一,经过数十年的发展已逐渐趋于成熟,并在各种功能分子的合成中获得了极为广泛的应用.近年来,随着光催化的兴起,可见光诱导的钯催化Heck反应也随之快速发展起来.作为一种新颖的C—C键构建策略,可见光诱导的Heck反应极大地扩展了底物的适用范围,包括亲核试剂和亲电试剂.同时,这种由激发态钯络合物引发,机理上涉及杂化的自由基-PdⅠ物种的特殊反应路径也使得可见光诱导的钯催化Heck反应表现出条件温和、官能团兼容性好以及转化多样性等特点,是对经典Heck反应的极大补充,在功能分子的合成以及复杂化合物的后期修饰等方面极具应用潜力.根据反应亲核/亲电试剂种类,以及串联反应类型,对可见光诱导的Heck反应进行归类和总结,并对部分反应机理进行了简要阐述.     

钯催化烯基苯并噁嗪酮基于内球型机理的线性和不对称烯丙基烷基化反应

烯基苯并噁嗪酮作为底物参与反应受到有机合成工作者的广泛关注.在过渡金属催化作用下,烯基苯并噁嗪酮脱除一分子二氧化碳,生成的两性离子中间体既可以被亲核试剂进攻,得到结构丰富的芳香胺,也可以作为1,4-偶极子与硫叶立德,缺电子烯烃或α,β-不饱和醛参与成环,分别生成相应的五元、六元或七元含氮杂环.后者广泛存在于农药、医药和生物活性分子中.已报道的钯催化烯基苯并噁嗪酮的不对称转化反应中,支链结构是主产物,线性结构产物比较少见.这是因为烯丙基邻位的氨基负离子与亲核试剂存在氢键或者静电作用,诱导亲核试剂进攻位阻更大但是能量更低的苄位.不同于传统的钯催化烯丙基取代反应,产物的结构通常是由亲核试剂的软硬程度决定.除了化学选择性的问题,产物中双键的Z/E构型和立体选择性的控制也同样成为挑战.近期Li课题组(Org.Lett.,2016,18,4392–4395)基于定位基辅助的Rh(Ⅲ)催化C?H活化策略实现了芳烃烯丙基化得到线性产物.Shi课题组(Chem.Commun.,2019,55,1283–1286)利用Ir(Ⅰ)和Br?nsted酸协同催化实现了吖内酯进攻端位烯丙基.但是,这些反应仅能得到消旋产物.发展不对称的线性烯丙基取代反应,不仅可以拓展烯基苯并噁嗪酮的应用前景,还可以合成具有手性的邻乙烯基芳香胺.本文采用α-硫氰基取代的茚酮作亲核试剂,不同于以往文献报道的机理,氨基负离子对烯醇式茚酮没有起到导向作用,意外得到以直链为主的产物.经过优化,最终以联萘二酚骨架亚膦酰胺为配体,钯作为催化剂,成功构建了一系列与硫氰基直接相连的季碳手性产物.所有反应产物均有优秀的化学选择性(线性选择性>20/1),E/Z选择性(>20/1)和立体选择性(最高95%ee).并且该反应适用范围广泛,基团的兼容性良好.为解释实验结果,本文进行相关的控制实验和DFT计算.计算结果表明,由于氨基负离子碱性较强,茚酮α位C?H酸性较强,直接发生了质子转移生成茚酮烯醇负离子,此时氢键作用消失不能起到导向作用.本文还考察了茚酮烯醇负离子与烯丙基钯通过静电作用形成离子复合物.与之前文献报道不同,本文采用了单齿膦配体且钯与配体等量,这意味着钯处于配位不饱和状态,导致离子复合物极其不稳定,烯醇负离子与硫氰基直接与钯配位成键,该过程结合能高达23.47 kcal/mol.最终配合物中间体通过内球型机理,经历环状过渡态得到以线性为主的产物.     

钯催化剂催化交叉偶联反应形成P-C键和复杂含磷化合物的研究进展

综述了利用金属钯催化交叉偶联反应形成P-C键以合成各种复杂的含磷化合物特别是手性膦配体的研究进展;介绍了参加偶联反应的不同价态的P化合物亲核试剂,以及卤代烯烃、卤代芳烃、三氟甲磺酸烯基脂、三氟甲磺酸芳基脂、乙烯基硼酸脂等亲电试剂;探讨了相应的偶联反应的反应条件、反应机理及其在材料、医药、农药等领域的应用.     

Development of catalytic asymmetric reactions via chiral palladium enolates

This article describes the generation of chiral palladium enolates and their application to several kinds of catalytic asymmetric reactions. Two methods to generate chiral enolates were developed using novel cationic palladium complexes 1 and 2 . In these processes, water or a hydroxo ligand on palladium metal plays an important role as a nucleophile to promote the transmetallation or as a Brønsted base to abstract an acidic α‐proton of the carbonyl group. These enolates showed sufficient reactivity with various electrophiles. Using a chiral Pd enolate as a key intermediate, highly enantioselective reactions such as catalytic aldol reactions, Mannich‐type reactions, Michael reactions, and fluorination reactions were developed. The unique structures of the palladium enolate complexes were elucidated and reaction mechanisms are proposed. © 2004 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 4: 231–242; 2004: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20017     

Enantioselective decarboxylative alkylation reactions: catalyst development, substrate scope, and mechanistic studies

α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.     

Synthesis of dihydroindenofuran scaffold via a Pd-catalyzed 5-endo-trig cyclization/enolate O-alkylation cascade

An efficient synthesis of dihydroindenofurans was carried out starting from the Baylis-Hillman adducts via a Pd-catalyzed 5-endo-trig-carbopalladation and enolate O-alkylation cascade as a key step. This is the first example of enolate O-alkylation with a C(sp³)-bound palladium intermediate.     

An aryl to imidoyl palladium migration process involving intramolecular C-H activation

Biologically interesting fluoren-9-one and xanthen-9-one derivatives have been prepared by a novel aryl to imidoyl palladium migration, followed by intramolecular arylation. The fluoren-9-one synthesis appears to involve both a palladium migration mechanism and a C-H activation process proceeding through an unprecedented organopalladium(IV) hydride intermediate. The results from deuterium labeling experiments are consistent with the proposed dual mechanism.     

Of the ortho effect in palladium/norbornene-catalyzed reactions: a theoretical investigation

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.     

Thermal studies on palladium alkyl xanthates

Eleven palladium(II) alkylxanthates: Pd(ROCSS)₂ [RMe, Et, nPr, iPr, nBu, iBu, tBu, nAm, iAm, nHex and cyclohex], have been prepared and their thermal properties investigated by thermogravimetric analysis. The complexes, although volatile under vacuum (10^?2 mm Hg), decompose without volatilization at normal atmospheric pressure leaving a residue of palladium metal at 950°C. The intermediate decomposition products were identified mass spectrometrically and a thermal decomposition mechanism is proposed.     

Palladium Enolate Umpolung: Cyclative Diacetoxylation of Alkynyl Cyclohexadienones Promoted by a Pd/SPRIX Catalyst

A novel palladium‐catalyzed reaction involving an unusual nucleophilic attack on a palladium enolate was developed using a spiro‐bis(isoxazoline) (SPRIX) ligand. Treatment of alkynyl cyclohexadienone substrates with a Pd/SPRIX catalyst in acetic acid under an oxygen atmosphere furnished diacetoxylated benzofuranone derivatives in good yields. This cyclative diacetoxylation proceeded enantioselectively in the presence of an optically pure SPRIX ligand.     

Divergent function in the crotonase superfamily: an anhydride intermediate in the reaction catalyzed by 3-hydroxyisobutyryl-CoA hydrolase

3-Hydroxyisobutyryl-CoA hydrolase (HICH), a member of the enoyl-CoA (crotonase) superfamily, catalyzes the hydrolysis of 3-hydroxyisobutyryl-CoA to 3-hydroxyisobutyrate. Like other members of the superfamily, the sequence of HICH contains conserved sequences for an oxyanion hole that stabilizes anionic intermediates. In contrast to most members of the superfamily, the reaction catalyzed by HICH does not proceed via formation of a thioester enolate anion; instead, evidence based on substrate deuterium isotope effects, the reactivity of substrate analogues that cannot form thioester enolate anions, single-turnover experiments in H218O, and the kinetic phenotypes of site-directed mutants provide evidence for a mechanism involving the formation of an anhydride intermediate involving Glu143 in the active site. In the reactions catalyzed by many members of the superfamily, homologues of Glu143 abstract the alpha proton of the thioester substrate to generate the thioester enolate anion intermediate. Presumably, one or more of the anionic tetrahedral intermediates on the HICH reaction coordinate are stabilized by the oxyanion hole. Thus, we conclude that the conserved oxyanion hole in this superfamily can be used to stabilize a variety of anionic intermediates.     

Mesoporous palladium-the surface electrochemistry of palladium in aqueous sodium hydroxide and the cathodic reduction of nitrite

The voltammetry of nanostructured palladium layers electrodeposited from a hexagonal liquid crystal phase onto platinum microdiscs show well defined peaks for the adsorption/desorption of hydrogen and surface oxidation/reduction in 2 M NaOH. These peaks are more clearly resolved than at smooth palladium and reveal the complications associated with hydrogen adsorption/desorption on palladium in aqueous alkaline solutions. The reduction of nitrite at the nanostructured palladium is also reported and it is shown that it occurs via a mechanism involving a chemical reaction between adsorbed hydrogen and adsorbed nitrite ion.     

A joint experimental and theoretical study of the palladium-catalyzed electrophilic allylation of aldehydes

Palladium-catalyzed electrophilic allylation of aldehydes with allylstannanes has been proposed in the literature as a model reaction illustrating the potential of nucleophilic eta(1)-allyl palladium pincer complexes to promote new catalytic processes. This reaction was studied by a joint experimental and theoretical approach. It was shown that pincer palladium complexes featuring a S approximately P approximately S and a S approximately C approximately S tridentate ligand are efficient catalysts for this reaction. The full mechanism of this transformation was studied in detail by means of DFT calculations. Two pathways were explored: the commonly proposed mechanism involving eta(1)-allyl palladium intermediates and a Lewis acid promoted mechanism. Both of these mechanisms were compared to the direct transformation that was shown experimentally to occur under mild conditions. The mechanism involving an eta(1)-allyl palladium intermediate has been discarded on energetic grounds, the nucleophilic attack and the transmetalation step being more energetically demanding than the direct reaction between allyltin and the aldehyde. On the other hand, a mechanism where the palladium acts as a Lewis acid proved to be fully consistent with all experimental and theoretical results. This mechanism involves (L approximately X approximately L)Pd(+) species which activate the aldehyde moiety toward nucleophilic attack.