Stereoselective synthesis of C15C24 and C25C30 fragments of dolabelides

The stereocontrolled synthesis of a C15C24 fragment of dolabelides is reported. The C19 and C21 hydroxyl-bearing stereocenters were installed using ruthenium-mediated asymmetric hydrogenations of cyclic hemiketal 4 and β-keto ester 7. The C25C30 portion of dolabelides was prepared as well by ring opening of chiral epoxy alcohol 12 to set up the C27 stereogenic center.     

CC bond formation in diiron complexes

The growing effort to design new sustainable synthetic methodologies, based on readily available and environmentally friendly transition metals, has boosted research on iron complexes. This review article focuses on C?C-bond-forming reactions occurring at bridging ligands in diiron complexes, aimed at evidencing distinctive aspects and advantages associated with the presence of two adjacent iron centres. A number of diiron-mediated C?C-bond-forming reactions reported in the literature, including nucleophilic and electrophilic additions and insertion and cycloaddition reactions, have been accumulated over the years, which, together with more recent developments, indicate that diiron complexes might provide promising alternatives to precious metals in the challenging field of metal-promoted C?C bond formation.     

Reversible Boron-Insertion into Aromatic C−C Bonds

Formation of borabicyclo[3.2.0]heptadiene derivatives was achieved via boron-insertion into aromatic C−C bonds in the photo-promoted skeletal rearrangement reaction of triarylboranes bearing an ortho-phosphino substituent (ambiphilic phosphine-boranes). The borabicyclo[3.2.0]heptadiene derivatives were fully characterized by NMR and X-ray analyses. The dearomatized products were demonstrated to undergo the reverse reaction in the dark at room temperature, realizing photochemical and thermal interconversion between triarylboranes and boron-doped bicyclic systems. Experimental and theoretical studies revealed that sequential two electrocyclic reactions involving E/Z-isomerization of an alkene moiety proceed via a highly strained trans-borepin intermediate.     

Transition Metal-Free Aromatic C−H,C−N,C−S and C−O Borylation

Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required.     

球状碳：C60及C70

本文简要介绍第三种形式的碳——C_(60)及C_(70)的发现过程、实验室制备、结构与光谱特征及形成球状Cn分子的一般原则;在最后部分,扼要提出了C_(60)的应用和研究前景。     

生物质转化中C―O/C―C键的活化断裂

生物质作为自然界中唯一可持续的有机碳来源,在解决环境和能源问题、创建一个碳中和的社会方面展现出巨大的潜力。木质生物质是由具有C―O/C―C键的基本结构单元构成的高分子化合物,活化、断裂这些C―O/C―C键是生物质高值化利用的关键,因此在过去十年中受到了广泛的关注。本文首先简要综述了生物质转化中C―O/C―C键催化断裂的现状,主要关注C―O/C―C键断裂的关键挑战和现有策略。我们的目标不是全面概述C―O/C―C键活化断裂的现况,而是提出与C―O/C―C键断裂相关的核心问题并且对未来的研究作出展望。我们选择了碳水化合物和木质素中几种具有代表性的C―O/C―C键来讨论它们在不同情况下协同催化断裂的机理,然后对未来的研究提出自己的见解。     

生物质转化中C―O/C―C键的活化断裂

Sustainable fuels and chemicals are receiving unprecedented attention worldwide in the context of achieving global carbon neutrality. Biomass, as the only natural and sustainable carbon-based source, shows great potential in addressing our current environmental/energy problems and in creating a carbon-neutral society. Lignocellulosic biomass is made up of basic structural units containing C―O/C―C bonds, and the catalytic cleavage of these C―O/C―C bonds is the key for biomass valorization; thus, garnering considerable attention in the past decade. This viewpoint begins with a brief report on the current status of catalytic activation/cleavage of C―O/C―C bonds during biomass conversion, and then goes on to discuss the key challenges experienced and possible strategies that can be implemented using cooperative catalysis. Our goal is not to provide a comprehensive overview of the activation/cleavage of the C―O/C―C bonds in biomass, but rather to highlight the core questions and challenges related to this process and the requirements for future investigations. We selected several representative C―O/C―C bonds in carbohydrates and lignin to discuss their catalytic mechanism in terms of total/selective bond cleavage, and then present our own insights for future studies. Therefore, this article mainly discusses the following two aspects: (1) The activation and cleavage of C―O bonds, which includes total and selective C―O bond cleavage in furan-based fuel precursors and lignin. When aiming to produce liquid fuels, including alkanes and arenes from biomass, the total cleavage of C―O bonds is essential. During the hydrodeoxygenation (HDO) of furan-based fuel precursors, various C―O bonds need to be cleaved, especially the C―O bond of each tetrahydrofuran ring, which has the highest bond energy. When compared with the total HDO of fuel precursors, the removal of the phenolic hydroxyl groups in lignin to produce arenes is more challenging because of the competition between the over-hydrogenation of the benzene rings and the cleavage of phenolic C―O bonds. The selective or partial cleavage of C―O/C―C bonds to form highly functionalized chemicals has recently attracted great interest and is believed to be a dynamic future research avenue. For example, the production of phenol from lignin or lignin-model compounds, through the selective removal of methoxy groups and para-side-chain groups, while preserving the phenolic hydroxyl groups, has been extensively explored in the past few years. (2) The other important aspect of this article is the cleavage of the C―C bonds in carbohydrates and lignin. The cleavage of carbohydrate C―C bonds occurs via retro-aldol condensation, which produces propylene glycol, ethylene glycol, ethanol, and lactic acid. The cleavage of C―C bonds in lignin is challenging because the bond energy of the C―C bonds is generally higher than that of the C―O bonds in lignin. Therefore, in this section, we discuss the cleavage of the strongest 5―5' bond in lignin. Finally, some subjective perspectives and future directions are provided, also highlighting several major challenges in this field.      

可见光诱导C—N键断裂构建C—C键的研究进展

近年来,可见光促进的光化学有机转化引起了广大有机化学家的兴趣.相比于传统方法,利用可见光作为可再生能源的光氧化还原催化已被证明是一种温和而强大的工具,可以通过单电子转移(SET)过程促进有机分子的活化.在许多天然产物的结构中存在大量的氨基功能团,同时氨基也是一些药物分子和功能材料的重要结构单元.因此,通过对这些物质分子中的C—N键进行活化而进行C—C键形成的偶联反应,则可以对该类化合物进行有效的结构修饰,从而得到具有多种结构及功能化的化合物.因此,这方面的研究现已成为了有机合成的一个重要研究领域.综述了近年来通过可见光促进C—N键断裂及其在C—C键形成反应研究中的应用研究成果,讨论了代表性的例子及其反应机制.     

Recent advances in radical-mediated fluorination through C–H and C–C bond cleavage

The C–H and C–C bonds are abundant in organic compounds, yet generally inert in chemical transformations. Therefore, direct functionalization of inert chemical bonds remains challenging. The fluorine-containing compounds are of special interest for their uses in medicinal chemistry. Direct fluorination of C–H and C–C bonds undoubtedly represents one of the most ideal and attractive approaches to incorporate fluorine atom into complex molecules. Herein, we summarize the recent advances in radical-mediated C–H and C–C bond fluorination. Three types of transformations are discussed: (1) direct C–H abstraction/fluorination of alkanes; (2) decarboxylative fluorination of alkyl carboxylic acids; (3) ring-opening fluorination.     

Electronic structures of C36 fulleride anions: C36− and C362−

Electronic structures for mono- and dianionic species of two promising C₃₆ fullerene isomers, 14 and 15, are investigated by means of the hybrid Hartree–Fock (HF)/density functional (DF) method. Structural deformations, charge distributions, and spin densities upon one- or two-electron reduction are explained in light of the lowest unoccupied molecular orbitals (LUMOs) of each neutral isomer. First electron affinities for the neutral isomers 14 and 15 are predicted to be 2.3 and 2.5 eV, respectively, facilitating n-type doping for C₃₆ solids. The degrees of local aromaticity of the isomers 14 and 15 tend to decrease with reduction in contrast with C₆₀.     

An improved synthesis of the C42–C52 segment of ciguatoxin 3C

In our previously reported method for the construction of the IJKLM-ring of ciguatoxin 3C (CTX3C), the lengthy synthetic process for the intermediate C42–C52 (L-ring) segment was problematic. Therefore, a new and improved procedure for the C42–C52 segment, having modified protecting groups, was developed. The new route includes a chirality transferring Ireland-Claisen rearrangement for the construction of the vicinal dimethyl branching at C47–48, a one-pot cyclization process for the establishment of the stereocenters at C45 and C46 as well as the γ-hydroxy δ-lactone framework corresponding to the L-ring, and Brown’s asymmetric crotylboration for the installation of the stereocenters at C43 and C44. The new C42–C52 segment was successfully coupled with the previously reported C32–C41 (I-ring) segment to produce the IJKLM-ring.     

C50富勒烯及其二聚物C100、C101的光学性质

运用B3LYP方法在6-31G*基组水平上对C50富勒烯以及它的两个不同二聚物C100、C101的几何构型进行了全优化. 在优化所得构型的基础上, 采用TDB3LYP方法在3-21G*基组水平上对其激发态性质、电子吸收光谱进行了研究, 根据计算得到的态态间跃迁偶极矩和跃迁能等数据, 结合使用态求和公式进一步计算得到了它们不同光学过程中的三阶非线性极化率. 结果表明, 当C50富勒烯二聚以后, 其电子吸收光谱的最大波长吸收峰发生了明显的红移, 三阶非线性极化率有了较大的提高. 其中, [5,5]-[5,5]哑铃型二聚物C101有着比[2+2]闭环型二聚物C100更大的三阶非线性极化率.     

Divergent Coupling of Benzocyclobutenones with Indoles via C−H and C−C Activations

Highly selective divergent coupling reactions of benzocyclobutenones and indoles, in which the chemoselectivity is controlled by catalysts, are reported herein. The substrates undergo C2(indole)–C8(benzocyclobutenone) coupling to produce benzylated indoles and benzo[b]carbazoles in the Ni- and Ru-catalyzed reactions. A completely different selectivity pattern C2(indole)–C2(benzocyclobutenone) coupling to form arylated indoles is observed in the Rh-catalyzed reaction. Preliminary mechanistic studies suggest C−H and C−C activations in the reaction pathway. Synthetic utility of this protocol is demonstrated by the selective synthesis of three different types of carbazoles from the representative products.     

镍催化C—C键活化反应研究进展

过渡金属催化C—C键活化是有机化学一个热点和难点领域,吸引着人们广泛的关注.C—C键活化可以为很多复杂分子的合成提供简单、快速和原子经济性的方法.相比于钯、铑和铱等过渡金属催化剂,镍催化剂有很多优点,更加经济适用,也表现出独特的催化活性,备受化学家们的青睐.主要介绍了近些年镍催化C—C键断裂反应的研究进展.     

C60和C70的分子及晶体结构

本文较详细地介绍了Ｃ６０、Ｃ７０的各种光谱、波谱、Ｘ射线衍射结果及Ｃ６０、Ｃ７０单晶体的培养方法,说明了Ｃ６０、Ｃ７０的分子构型及晶体结构和相变特点。     

C1化学

以ＣＯ／Ｈ２、ＣＨ３ＯＨ、ＣＨ４、ＣＯ２为主要原料的Ｃ１化学，将在本世纪末或下世纪初兴起，发展Ｃ１化学可以缓解日趋枯褐的石油资源危机，延续人类不可缺少的能源及化工生产。本文概述了Ｃ１化学的发展现状及研究方向，展现了Ｃ１化学的基本框架。同时，还从能源、资源、经济、生态等方面论述了发展Ｃ１化学的重要意义：未来的世界必须发展Ｃ１化学，Ｃ１化学必将为未来世界造福。     

富勒烯C60／C70的制备化学

评价了富勒烯制备化学的研究与进展，阐述了未来工业规模生产富勒烯的发展动向与前景，着重对有机合成制备Ｃ６０的研究进行了探讨。     

金催化的C—C偶联反应研究进展

近年来金催化剂作为一种温和的π路易斯酸展现了其独特的催化性能,已经成为有机化学研究的热点之一.综述了近年来金催化的碳碳偶联反应,并对其以后在氧化还原反应方面的应用进行探讨.