亮点介绍

正镍催化不对称分子内氢烯基化反应J. Am. Chem. Soc. 2018, 140, 7458～7461过渡金属催化的氮原子或氧原子连接的不饱和底物的对映选择性环化是构筑手性含氮杂环或含氧杂环的直接方法.文献中,人们已经发展了多种手性过渡金属催化剂,实现了氮原子或氧原子连接的烯-炔和联烯-炔的高对映选择性环化反应,然而,对于相应的二烯对映选择性环化鲜有成功的例子.最近,周其林、朱守非团队发展了手性螺     

分子内Friedel-Crafts环化反应在苯并环状物合成中的应用

Friedel-Crafts反应是有机合成中最有用的反应之一,它的应用范围十分广泛.Friedel-Crafts反应也是合成环状化合物的重要途径,尤其分子内的环化反应一直以来受到广泛的关注.对近年来应用分子内Friedel-Crafts环化反应合成苯并环状化合物进行了详细的综述,并对分子内Friedel-Crafts环化反应在有机合成上发展前景作了展望.     

氮自由基启动的1,n-烯炔环化反应

C–N键广泛存在于药物、天然产物和功能材料中,而氮中心自由基在C–N键的构建中起到关键作用.但是,与广泛使用的碳中心自由基相比,氮中心自由基由于缺乏实用简便的产生方法而尚未得到充分研究.因此,发展高效的氮中心自由基引发反应迫在眉睫.在过去的几年里,得益于可信赖且可控制的自由基化学的兴起,可以通过热分解、氧化剂促进、金属盐催化或电催化来产生氮中心自由基.1,n-烯炔环化不仅可以一步反应同时构建形成两个或多个新的化学键,而且可以高选择性引入各种外部官能团,被认为是构建复杂环状化合物必不可少的方法.传统上,通过贵金属(例如Au、Pd、Rh、Ru等)和/或引发剂介导/催化来实现1,n-烯炔环化反应.1985年,Curran和他的同事报道了具有里程碑意义的工作,该方法通过碘代烯炔类化合物的分子内自由基串联环化反应实现了(±)-hirsutene的简洁全合成.受该工作的启发,并伴随着现代合成技术的发展,自由基启动的1,n-烯炔环化由于反应条件温和、具有较高的官能团兼容性、原子利用率高、通常不使用化学计量的金属催化剂和/或有毒引发剂,因而受到化学家们越来越多的关注.在此背景下,化学工作者已经开发了多种氮中心自由基启动的1,n-烯炔类化合物环化反应的方法.然而,据我们所知,目前还没有专门针对该主题的综述,因此本文及时进行总结分析.迄今为止,氮中心自由基启动的1,n-烯炔环化反应大概分为三种途径:(1)氮中心自由基选择性的与1,n-烯炔的C=C键进行加成反应,然后通过分子内环化以生成烯基自由基中间体,最后借助进一步环化反应、氢原子攫取或自由基偶联以得到最终产物;(2)涉及到氮中心自由基与1,n-烯炔的C≡C键的选择性加成反应、分子内环化及氧化脱氢;(3)借助分子内原位生成的氮中心自由基来启动的,随后经过两次分子内环化、单电子转移氧化及脱氢反应转化为最终产物.本文将依据氮中心自由基的类型,分为硝基自由基、叠氮自由基和酰胺自由基进行讨论,并将重点放在生成氮中心自由基的方法及其环化模式、相关反应机理以及存在的挑战上.     

Wen‐Ting Wei a,*, Qiang Li a,b, Ming‐Zhong Zhang c,Wei‐Min He d,#

C–N键广泛存在于药物、天然产物和功能材料中,而氮中心自由基在C–N键的构建中起到关键作用.但是,与广泛使用的碳中心自由基相比,氮中心自由基由于缺乏实用简便的产生方法而尚未得到充分研究.因此,发展高效的氮中心自由基引发反应迫在眉睫.在过去的几年里,得益于可信赖且可控制的自由基化学的兴起,可以通过热分解、氧化剂促进、金属盐催化或电催化来产生氮中心自由基.1,n-烯炔环化不仅可以一步反应同时构建形成两个或多个新的化学键,而且可以高选择性引入各种外部官能团,被认为是构建复杂环状化合物必不可少的方法.传统上,通过贵金属(例如Au、Pd、Rh、Ru等)和/或引发剂介导/催化来实现1,n-烯炔环化反应.1985年, Curran和他的同事报道了具有里程碑意义的工作,该方法通过碘代烯炔类化合物的分子内自由基串联环化反应实现了(±)-hirsutene的简洁全合成.受该工作的启发,并伴随着现代合成技术的发展,自由基启动的1,n-烯炔环化由于反应条件温和、具有较高的官能团兼容性、原子利用率高、通常不使用化学计量的金属催化剂和/或有毒引发剂,因而受到化学家们越来越多的关注.在此背景下,化学工作者已经开发了多种氮中心自由基启动的1,n-烯炔类化合物环化反应的方法.然而,据我们所知,目前还没有专门针对该主题的综述,因此本文及时进行总结分析.迄今为止,氮中心自由基启动的1,n-烯炔环化反应大概分为三种途径:(1)氮中心自由基选择性的与1,n-烯炔的C=C键进行加成反应,然后通过分子内环化以生成烯基自由基中间体,最后借助进一步环化反应、氢原子攫取或自由基偶联以得到最终产物;(2)涉及到氮中心自由基与1,n-烯炔的C≡C键的选择性加成反应、分子内环化及氧化脱氢;(3)借助分子内原位生成的氮中心自由基来启动的,随后经过两次分子内环化、单电子转移氧化及脱氢反应转化为最终产物.本文将依据氮中心自由基的类型,分为硝基自由基、叠氮自由基和酰胺自由基进行讨论,并将重点放在生成氮中心自由基的方法及其环化模式、相关反应机理以及存在的挑战上.     

氮自由基环化反应的新进展

三十年前,自由基反应在有机合成中的应用已经非常普遍,但其主要集中在碳自由基的应用上,而杂原子自由基却一直得不到发展.氮自由基环化反应是在近十年内才逐步应用到有机合成中的,它对合成一系列的氮杂环化合物有重要的意义,如内酰胺类、吡咯烷类、生物碱类物质等.从四个方面对氮自由基经环化反应合成多种氮杂环化合物的研究进展做一介绍.     

通过电化学C—H/N—H官能团化合成多取代吲哚和氮杂吲哚

正Angew.Chem.Int.Ed.2016,55,9168~9172吲哚和氮杂吲哚结构是多种天然产物和药物分子的核心结构,发展合成这类结构的高效、绿色合成方法学具有重要的意义.厦门大学固体表面物理化学国家重点实验室徐海超和吕鑫等利用电化学方法实现了分子内芳胺和炔烃的[3+2]环化反应.该环化反应既可用于合成高取代吲哚,也可得到合成上具有挑战性的复杂氮杂吲哚.该反应是     

锌催化异噁唑和烯炔醚的不对称6π电环化反应

正6π电环化反应具有高立体选择性、高原子经济性等优点,可用于高效构建五至七元环状化合物;相关研究方法已被广泛应用于天然产物和生物活性分子的合成.近年来有关发展高效的6π电环化反应研究受到了广泛的关注.就反应机理而言,该环化反应可经由戊二烯阴     

吲哚苄位碳正离子引发的串联环化反应的普适性和机理探究

对在α-环匹阿尼酸(α-CPA)和speradineC全合成中发展的仿生吲哚苄位碳正离子引发的串联环化反应的普适性和机理进行了研究,实验结果表明,该苄位碳正离子串联环化反应在含有吲哚的底物中能顺利发生,说明吲哚氮原子的共轭效应在吲哚苄位碳正阳离子串联环化反应中起到了关键性的作用.     

基于α-氢迁移策略构建杂环骨架的研究进展

杂环化合物的高效构建是有机合成领域的重要课题,[m+n]环化反应可将两个相对简单易得的反应底物进行组合,是构建环状骨架的重要手段.基于负氢迁移策略的[m+n]环化反应将两个相对易得的底物原位生成负氢受体,避免反应底物的预制,具有高的原子和步骤经济性.选取基于负氢迁移策略的[m+n]环化反应为研究对象,从通过该类反应所构建的氮杂、氧杂环骨架着手,按照生成氮杂、氧杂环的大小进行分类,综述了2018年以来基于负氢迁移策略的[m+n]环化反应的研究进展,并对该领域的发展方向进行了展望.     

钡原子对Ru（0001）表面氮分子吸附和解离过程的影响

采用密度泛函理论方法研究了钡原子对Ru（0001）表面氮分子解离过程的影响.计算结果表明：在Ru（0001）表面,钡原子失去电子后形成Ba（1＋δ）＋阳离子.表面转移电荷增强了衬底钌原子d轨道和氮分子π轨道间的杂化作用以及氮分子内的库仑排斥作用,减弱了氮分子键.在钡原子的作用下,γ态氮分子键键长从0.113 nm增加到...     

Syntheses of β-amidovinyltellurides and oxazoles by addition reactions of alkynes with benzenetellurinyl trifluoromethanesulfonate in acetonitrile

Benzenetellurinyl trifluoromethanesulfonate in conjunction with acetonitrile readily effected amidotellurinylation reactions with alkynes. Most of the addition reactions proceeded in a trans fashion to form the (E)-β-acetamidovinyl phenyl telluroxides. Subsequently, it was found that the prevailing Markovnikov adducts from terminal alkynes immediately isomerized to (Z)-isomers which were isolated as the corresponding vinyltellurides. On the other hand, the adducts derived from internal alkynes thermally underwent a spontaneous intramolecular cyclization to be transformed eventually into oxazoles.     

Palladium(II)-catalyzed enyne coupling reaction initiated by acetoxypalladation of alkynes and quenched by protonolysis of the carbon-palladium bond

[reaction: see text] Divalent palladium-catalyzed inter- and intramolecular enyne coupling reactions initiated by acetoxypalladation of alkynes were developed. The reaction involves the acetoxypalladation of the alkyne, followed by the insertion of the alkene and the protonolysis of the carbon-palladium bond. The protonolysis of the carbon-palladium bond in the presence of bidentate nitrogen containing ligands is the key step in completing the Pd(II) catalytic cycle. The nitrogen-containing ligands, like halides, served to favor the protonolysis of the carbon-palladium bond over the beta-H elimination in the Pd(II)-mediated reactions. The intermolecular coupling reactions provide an efficient method for synthesizing gamma,delta-unsaturated carbonyls. The intramolecular coupling reactions offer a method to construct a variety of synthetically important carbo- and heterocycles. The asymmetric version of such a cyclization was developed with moderate enantioselectivity when employing pymox (pyridyl monooxazoline) as the ligand.     

Palladium-catalyzed intramolecular asymmetric hydroamination, hydroalkoxylation, and hydrocarbonation of alkynes

A conceptually novel approach for asymmetric intramolecular hydroamination, hydroalkoxylation and hydrocarbonation of alkynes using chiral palladium catalysts are described. The reactions of the aminoalkynes 5, alkynols 7, and alkynylmethines 9 in the presence of Pd2(dba)3 x CHCl3/PhCOOH/renorphos 4 in benzene (or benzene-hexane) at 100 degrees C gave the corresponding cyclization products (nitrogen heterocycles 6, oxygen heterocycles 8, and carbocycles 10) in good yields with good enantioselectivities. The origins of enantioselectivities in the hydroamination reaction are discussed based on DFT computations.     

Base-Promoted Difunctionalization of Alkynes: One-Pot Synthesis of Polysubstituted Chromones

A transition-metal-free one-pot procedure for the difunctionalization of alkynes by C−C triple bond oxidation and transformation towards chromone derivatives has been developed. It involves cascade reactions for carbonylation of alkynes, base-promoted C−C σ-bond cleavage, and intramolecular cyclization. This procedure provides an efficient protocol for the synthesis of polysubstituted chromones from readily available starting materials.     

Pd/Cu-catalyzed cascade Sonogashira coupling/cyclization reactions to highly substituted 3-formyl furans

An efficient palladium/copper-catalyzed approach to the synthesis of highly substituted 3-formyl furans from the reactions of readily available α-bromoenaminones with terminal alkynes has been developed. This methodology was realized by the cascade reactions of Sonogashira coupling and the subsequent intramolecular cyclization.     

Reaction between Azidyl Radicals and Alkynes: A Straightforward Approach to NH‐1,2,3‐Triazoles

Reaction between nitrogen‐centered radicals and unsaturated C?C bonds is an effective synthetic strategy for the construction of nitrogen‐containing molecules. Although the reactions between nitrogen‐centered radicals and alkenes have been studied extensively, their counterpart reactions with alkynes are extremely rare. Herein, the first example of reactions between azidyl radicals and alkynes is described. This reaction initiated an efficient cascade reaction involving inter‐/intramolecular radical homolytic addition toward a C?C triple bond and a hydrogen‐atom transfer step to offer a straightforward approach to NH‐1,2,3‐triazoles under mild reaction conditions. Both the internal and terminal alkynes work well for this transformation and some heterocyclic substituents on alkynes are compatible. This mechanistically distinct strategy overcomes the inherent limitations associated with azide anion chemistry and represents a rare example of reactions between a nitrogen‐centered radicals and alkynes.     

Alkynes and Nitrogen Compounds: Useful Substrates for the Synthesis of Pyrazoles

The easy preparation and functionalization of pyrazoles associated with their innumerable biological properties have made this class of N-heterocycles very attractive for the development of new synthetic routes and applications. The cyclization reactions of alkynes and nitrogen compounds represent a powerful tool for the preparation of pyrazoles. This Review covers the recent advances in the preparation of pyrazoles by reacting alkynes and nitrogen compounds under transition-metal-catalyzed or metal-free conditions.     

Manganese-Catalyzed Carbomagnesation of Alkynes

The development of manganese-catalyzed carbomagnesation of alkynes is reviewed. Manganese salts mediate the efficient addition of a variety of Grignard reagents to alkynes. Allyl, aryl, and alkyl Grignard reagents participate in these reactions. In many cases, a hetero atom such as oxygen or nitrogen in substrates facilitates the addition reaction. Stoichiometric carbometalation reactions with manganese ate complexes are also discussed, as is cyclization of 1,6-diynes and 1,6-enynes via carbometalation with triallylmanganate.     

Base-free NIS promoted electrophilic cyclization of alkynes: an efficient synthesis of iodo substituted pyrano[4,3-b]quinolines

A simple and mild procedure for the synthesis of iodo substituted 1H-pyrano[4,3-b]quinolines has been achieved using NIS reagent in the absence of base from 2-alkynylquinoline-3-carboxaldehydes via intramolecular electrophilic cyclization onto alkynes in good to excellent yields in a short duration of time. The reactions proceeded smoothly in a normal solvent in aerobic atmosphere at room temperature. The presence of substituent at either quinoline or alkyne moieties did not show effect on reaction rate of cyclization. The palladium-catalyzed transformations of iodo group to C-C bond are also discussed.     

Triethylsilane-indium(III) chloride system as a radical reagent

[reaction: see text] A novel generation method of indium hydride (Cl2InH) was found by the transmetalation of InCl3 with Et3SiH. In the intramolecular cyclization of enynes, the previously reported system (NaBH4-InCl3) has a problem of side reactions with the coexistent borane. In contrast, the problem was solved by the presented system, which affords effective hydroindation of alkynes.