Indole alkaloids synthesis via a selective cyclization of aminocyclopropanes

The continuous progress in medicinal chemistry requires more versatile synthetic strategies for the generation of large libraries of active compounds and their analogues. As a result, the research for new effective cyclization and cycloaddition reactions is an essential task in organic chemistry. In 2008 we developed the first catalytic formal homo-Nazarov reaction starting from activated cyclopropanes. Herein we report the extension of the catalytic formal homo-Nazarov cyclization to aminocyclopropanes. Highly diastereoselective cyclizations were obtained via an acyliminium intermediate generated through opening of the cyclopropane. An excellent control over the regioselectivity of either the C-C or C-N cyclization in the case of free indoles as nucleophilic partners was achieved. The utility of the developed methodology was demonstrated by the generation of the polycyclic scaffolds of Aspidosperma and Gonioma natural products starting from a common intermediate. Based on this method, a formal total synthesis of the alkaloid aspidospermidine and the total synthesis of the alkaloid goniomitine are presented. Finally, the scope and limitations of our methodology are discussed on an extended range of vinyl-cyclopropyl ketones with cyclic or acyclic carbamates, as well as ethers as donor groups on the cyclopropane.     

Cyclopropanes and hypervalent iodine reagents: high energy compounds for applications in synthesis and catalysis

One of the major challenges faced by organic chemistry is the efficient synthesis of increasingly complex molecules. Since October 2007, the Laboratory of Catalysis and Organic Synthesis (LCSO) at EPFL has been working on the development of catalytic reactions based on the Umpolung of the innate reactivity of functional groups. Electrophilic acetylene synthons have been developed using the exceptional properties of ethynyl benziodoxolone (EBX) hypervalent iodine reagents for the alkynylation of heterocycles and olefins. The obtained acetylenes are important building blocks for organic chemistry, material sciences and chemical biology. The ring-strain energy of donor-acceptor cyclopropanes was then used in the first catalytic formal homo-Nazarov cyclization. In the case of aminocyclopropanes, the method could be applied in the synthesis of the alkaloids aspidospermidine and goniomitine. The developed methods are expected to have a broad potential for the synthesis and functionalization of complex organic molecules, including carbocycles and heterocycles.     

微波促进有机合成与研究

微波辐射技术可用于多种有机反应,如氧化反应、缩合反应、还原反应、酯化反应、烃烷基化反应、烯烃加成反应、羰基加成-消除反应、重排反应、环化和开环反应、Diels-Alder成环反应、取代反应、脱保护基反应、酰基化反应、芳基化反应、自由基反应、Tipson Cohen反应、产生二氯卡宾反应、脱羧反应、磺化反应、催化氢化反应、Bischler Napieralski反应、Fries重排反应、偶合反应、Mannich反应及金属有机化合物的合成反应等。     

Reducing Product Inhibition in Nucleic Acid‐Templated Ligation Reactions: DNA‐Templated Cycligation

Programmable interactions allow nucleic acid molecules to template chemical reactions by increasing the effective molarities of appended reactive groups. DNA/RNA‐triggered reactions can proceed, in principle, with turnover in the template. The amplification provided by the formation of many product molecules per template is a valuable asset when the availability of the DNA or RNA target is limited. However, turnover is usually impeded by reaction products that block access to the template. Product inhibition is most severe in ligation reactions, where products after ligation have dramatically increased template affinities. We introduce a potentially generic approach to reduce product inhibition in nucleic acid‐programmed ligation reactions. A DNA‐triggered ligation–cyclization sequence (“cycligation”) of bifunctional peptide nucleic acid (PNA) conjugates affords cyclic ligation products. Melting experiments revealed that product cyclization is accompanied by a pronounced decrease in template affinity compared to linear ligation products. The reaction system relies upon haloacetylated PNA‐thioesters and isocysteinyl‐PNA‐cysteine conjugates, which were ligated on a DNA template according to a native chemical ligation mechanism. Dissociation of the resulting linear product‐template duplex (induced by, for example, thermal cycling) enabled product cyclization through sulfur‐halide substitution. Both ligation and cyclization are fast reactions (ligation: 86 % yield after 20 min, cyclization: quantitative after 5 min). Under thermocycling conditions, the DNA template was able to trigger the formation of new product molecules when fresh reactants were added. Furthermore, cycligation produced 2–3 times more product than a conventional ligation reaction with substoichiometric template loads (0.25–0.01 equiv). We believe that cyclization of products from DNA‐templated reactions could ultimately afford systems that completely overcome product inhibition.     

Tunable Phosphine‐Mediated Domino Reaction: Selective Synthesis of 2,3‐Dihydrofurans and Biaryls

We have developed a novel strategy to control the product distribution between 2,3‐dihydrofurans and biaryls from the same starting materials by tuning the catalytic or stoichiometric process. By controlling the loading of the phosphine PR₃, the Morita–Baylis–Hillman carbonates can be selectively used as a C₁ or a C₃ synthon, respectively. This investigation has given new insights into tunable domino reactions and will be useful in diversity‐oriented synthesis (DOS).     

Electrocatalytic tandem Knoevenagel-Michael reaction of 3-methyl-2-pyrazolin-5-ones, aryl aldehydes and cyano-functionalized C-H acids: Facile and convenient multicomponent way to substituted 3-(5-hydroxy-3-methylpyrazol-4-yl)-3-arylpropionitriles

Electrochemically induced catalytic tandem Knoevenagel-Michael reaction of 3-methyl-2-pyrazolin-5-ones, aryl aldehydes and malononitrile or alkyl cyanoacetates in alcohols in an undivided cell in the presence of sodium bromide as an electrolyte results in the formation of substituted 3-(5-hydroxy-3-methylpyrazol-4-yl)-3-arylpropionitriles in 75-97% yields. The developed efficient electrocatalytic approach to the corresponding 3-(5-hydroxy-3-methylpyrazol-4-yl)-3-arylpropionitriles is beneficial from the viewpoint of diversity-oriented large-scale processes and represents novel, facile and environmentally benign synthetic concept for multicomponent reactions strategy.     

Non-phosgene synthesis of hexamethylene-1,6-diisocyanate from thermal decomposition of hexamethylene-1,6-dicarbamate over Zn–Co bimetallic supported ZSM-5 catalyst

A non-phosgene route for the synthesis of hexamethylene-1,6-diisocyanate(HDI) was developed via catalytic decomposition of hexamethylene-1,6-dicarbamate(HDC) over Zn–Co bi-metallic supported ZSM-5 catalyst.The catalyst was characterized by FTIR and XRD analyses. Three solvents dioctyl sebacate(DOS), dibutyl sebacate(DBS) and 1-butyl-3-methylimidazolium tetrafluoroborate(BMIMBF_4) were investigated and compared; DOS gave better performance. The catalytic performances for thermal decomposition of HDC to HDI using DOS as solvent were then investigated, and the results showed that, under the optimized reaction conditions, i.e.,10 wt%concentration of HDC in DOS, 250 °C temperature, 60 min reaction time, 83.8% yield of HDI had been achieved over Zn–Co/ZSM-5. Decomposition of the intermediate hexamethylene-1-carbamate-6-isocyanate(HMI) over Zn–Co/ZSM-5 in DOS solvent was further studied and the results indicated that yield of HDI from HMI reached to 69.6%(98.6% HDI selectively) at 270 °C, which further increased the yield of the total HDI(HDI_(tol)) to as high as 95.0%. Recycling of catalyst showed that HDI and HMI yield slightly decreased, and by-product yield increased after the catalyst was reused for 4 times. At last possible reaction mechanism was proposed.     

Synthesis of Tropine-Based Functionalized Acidic Ionic Liquids and Catalysis of Esterification

Some traditional acidic ionic liquids (AILs) have shown great catalytic potential in esterification; meanwhile, the design and application of more new AILs are expected at present.Tropine-based functionalized acidic ionic liquids (FAILs) were synthesized to realize esterification catalysis for the first time; with aspirin synthesis as the template reaction, key influences on the substrate conversion and product yield of the synthesis, such as IL type, ratio of salicylic acid to acetic anhydride, temperature, reaction time and amount of IL, were investigated. The new tropine-based FAILs exhibited excellent performance in catalytic synthesis of aspirin with 88.7% yield and 90.8% selectivity. Multiple recovery and re-usage of N-(3-propanesulfonic acid) tropine is the cation, and p-toluenesulfonic acid is the anion. ([Trps][OTs]) shows satisfactory results. When [Trps][OTs] was used to catalyze different esterification reactions, it also showed good results. The above studies proved that ionic liquid [Trps][OTs] could serve as an ideal green solvent for esterification reaction, which serves as a suitable substitute for current catalysts.     

邻硝基乙苯法合成3-甲基吲哚

考察了3-甲基吲哚的合成路线。以氯霉素工业大量副产的邻硝基乙苯为原料,经缩合、催化氢化及催化环合三步反应成功合成了3-甲基吲哚,总摩尔收率69.5%。进一步研究表明,缩合反应必须采用强碱性催化剂如甲醇钠催化;铂炭或钯炭均不能有效催化2-(2-硝基苯基)-丙-1-醇的硝基还原反应,而骨架镍催化剂则是该反应的良好催化剂;在环合反应条件下,骨架镍催化剂具有良好的活性和稳定性。该法为3-甲基吲哚的合成提供了一条经济路线。     

6,7-二氢-5H-环戊烷并[b]吡啶的合成进展

6,7 二氢 5H 环戊烷并[b]吡啶具有抗溃疡、抗癌等重要生理活性,是合成头孢匹罗的重要原料。按热重排反应、催化脱水脱氢反应、Friedlander缩合反应、Grignard试剂环合反应、Diels Alder反应和1,5 二羰基化合物的环合等合成6,7 二氢 5H 环戊烷并[b]吡啶的反应类型进行分类,首次对其合成进展进行了全面的综述,认为以吡啶衍生物及1,5 二羰基化合物为原料合成6,7 二氢 5H 环戊烷并[b]吡啶的方法值得关注。     

Chemical Space Overlap with Critical Protein–Protein Interface Residues in Commercial and Specialized Small-Molecule Libraries

There is growing interest in the use of structure-based virtual screening to identify small molecules that inhibit challenging protein–protein interactions (PPIs). In this study, we investigated how effectively chemical library members docked at the PPI interface mimic the position of critical side-chain residues known as “hot spots”. Three compound collections were considered, a commercially available screening collection (ChemDiv), a collection of diversity-oriented synthesis (DOS) compounds that contains natural-product-like small molecules, and a library constructed using established reactions (the “screenable chemical universe based on intuitive data organization”, SCUBIDOO). Three different tight PPIs for which hot-spot residues have been identified were selected for analysis: uPAR⋅uPA, TEAD4⋅Yap1, and Ca_Vα⋅Ca_Vβ. Analysis of library physicochemical properties was followed by docking to the PPI receptors. A pharmacophore method was used to measure overlap between small-molecule substituents and hot-spot side chains. Fragment-like conformationally restricted small molecules showed better hot-spot overlap for interfaces with well-defined pockets such as uPAR⋅uPA, whereas better overlap was observed for more complex DOS compounds in interfaces lacking a well-defined binding site such as TEAD4⋅Yap1. Virtual screening of conformationally restricted compounds targeting uPAR⋅uPA and TEAD4⋅Yap1 followed by experimental validation reinforce these findings, as the best hits were fragment-like and had few rotatable bonds for the former, while no hits were identified for the latter. Overall, such studies provide a framework for understanding PPIs in the context of additional chemical matter and new PPI definitions.     

用于催化甲醇制烯烃的SAPO-34分子筛合成的研究进展

介绍了用于催化甲醇制烯烃的SAPO-34分子筛合成的研究近况。SAPO-34分子筛的合成过程是影响其晶粒尺寸、酸性强弱等物化性能的重要因素, 因而是影响其催化性能的关键因素。本文详细叙述了原料配比及其种类、模板剂、F^-等合成因素对SAPO-34分子筛物化性能及其MTO反应催化性能的影响。针对SAPO-34合成及其催化性能优化的新技术, 综述了SAPO-34分子筛的金属改性及其超声波、微波辅助合成的特点和效果, 指出通过研发新的模板剂及其助剂、改性或制备新工艺进而改善分子筛的酸性、提高其烯烃选择性、延长催化反应寿命、降低合成成本是SAPO-34今后研发的重要方向。     

1–氨基四唑的三步法合成与表征

研究了以苯甲醛、水合肼为原料,经缩合、成环和水解三步反应合成1–氨基四唑的方法,采用红外光谱、核磁共振、元素分析等对中间体及产物结构进行了表征。考察了缩合反应温度、成环反应中原甲酸三乙酯与苯甲醛腙的摩尔比对反应收率的影响,确定了最佳反应条件:缩合反应温度为0⁵℃,n(原甲酸三乙酯)∶n(苯甲醛腙)=1.8∶1。三步反应总收率为49.5%。     

Copper(II) Bromide/Boron Trifluoride Etherate‐Cocatalyzed Cyclization of Ketene Dithioacetals and p‐Quinones: a Mild and General Approach to Polyfunctionalized Benzofurans

A new application of copper(II) bromide‐activated ketene dithioacetals as nucleophiles in organic chemistry has been developed. Under the cocatalysis of copper(II) bromide (2.0 mol%) and boron trifluoride etherate (10 mol%), the conjugate addition and sequential cyclization of α‐electron‐withdrawing group‐substituted ketene dithioacetals with p‐quinones in acetonitrile at room temperature gave a variety of benzofurans. This formal [3+2] cycloaddition provides a general method for catalytic synthesis of polyfunctionalized benzofurans with the advantages of readily available starting materials, cheap catalysts, mild reaction conditions, good yields and wide range of synthetic potential for the benzofuran products. Further transformations of the resulting benzofurans to 2‐aminobenzofurans and benzofuro[2,3‐d]pyrimidine derivatives are also investigated.     

Intramolecular Base‐Free Sonogashira Reaction for the Synthesis of Benzannulated Chiral Macrocycles Embedded in Carbohydrate Templates

A base‐free, intramolecular Sonogashira reaction‐based general approach has been established for the diversity‐oriented synthesis (DOS) of fused bi‐ and tricyclic systems containing benzannulated, 10‐ to 13‐membered chiral macrocycles embedded in carbohydrate templates. Macrocycles with different ring sizes have been prepared by pre‐designing the chiral building blocks. Base‐sensitive groups like acetyl and TBDPS survived the reaction conditions.     

四种单萜类查尔酮的合成

以2, 4, 6-三羟基苯乙酮和柠檬醛为起始原料经过环化、羟醛缩合和催化加氢合成四种单萜类查尔酮;关键步骤2, 4, 6-三羟基苯乙酮和柠檬醛是在吡啶的催化下经过电子环化、质子迁移及Diels-Alder反应合成天然产物desbenzylidenerubramin (1),中间体1合成一种天然产物产物rubraine (2~5),其结构经~1H NMR和HREIMS表征。     

Palladium-catalyzed cyclization of propargylic compounds

Many groups have explored the scope of the palladium-based cyclization of propargylic compounds since Tsuji's first report in 1985. Through the proper positioning of an internal nucleophilic center and the judicious selection of an appropriate external nucleophile, the synthetic chemist can effectively assert control over the course of the reaction and its products. However, initial investigations were very limited: only heterocyclic compounds were originally synthesized. We have found the palladium-catalyzed cyclization of propargylic compounds to be a very efficient method for producing both carbocyclic and heterocyclic compounds. In this Account, we discuss the cyclization reactions of functionalized propargylic compounds with a variety of nucleophiles that we have developed over the past few years. We also review similar reactions reported by other groups. We focus here on the cyclization of functionalized propargylic compounds containing a carbon nucleophilic center that is in close proximity to the propargylic moiety. We conducted a detailed investigation of their cyclizations with carbon nucleophiles, with nitrogen nucleophiles, with oxygen nucleophiles, and without nucleophiles. We have developed several efficient and useful methods for the synthesis of indenes, naphthalenes, polycycles, and spirocyclic compounds. All of these reactions proceed satisfactorily under very mild conditions; high regio- and stereoselectivity have been observed as well. In the course of our studies, we provided the first demonstration of a novel tandem C-H activation/bis-cyclization reaction of propargylic compounds with terminal alkynes. In addition, we used external nucleophiles to investigate the cyclization of functionalized propargylic compounds that bear an unsaturated carbon-carbon or carbon-heteroatom bond. We presented the first report of the use of external nucleophiles to initiate a novel cyclization of functionalized propargylic compounds containing an electrophile. This revelation provided a fresh perspective through the discovery of a new type of domino cyclization of propargylic compounds. Metal-catalyzed cyclization of propargylic compounds can provide indenes, cyclopentanones, cyclic carbonates, benzofurans, and a range of other cyclic molecules. A thorough understanding of the mechanisms involved in this class of reaction affords exceptional synthetic control, as shown here by our development of efficient procedures and reagents for palladium-catalyzed propargylic cyclizations.     

Methyl formate as a new building block in C1 chemistry

Methyl formate has been proposed as a building block molecule in C₁ chemistry. This paper examines the potential of this concept by reviewing the processes of synthesis of the molecule and the chemical reactions that it undergoes. Methyl formate can be produced by a variety of routes from a number of feedstocks. The reaction between methanol and carbon monoxide is an efficient process, used commercially. Combination of an efficient synthesis of methyl formate and its facile decomposition allows the molecule to be used as a means for separation, storage and transport of synthesis gas. The number of reactions that convert methyl formate to other chemicals is large. In particular, the synthesis of large volume chemicals such as methanol, acetic acid and ethylene glycol deserves serious consideration. Examples are provided of applications in the chemical and energy industries involving methyl formate. The reactions involved in the synthesis and transformation of methyl formate are mostly catalytic in nature. Many currently known catalytic systems are not efficient to compete with conventional routes involving methanol or synthesis gas. Fundamental research to understand the catalytic chemistry involved is highly desirable in order to improve the performance of the catalytic systems.     

目标导向合成及差异导向合成在药物合成中的应用

介绍了目标导向合成和差异导向合成的基本概念,扼要阐述了目标导向合成在药物合成上的应用,着重综述了差异导向合成的固相有机合成法和液相有机合成法在合成有机小分子库以备药物筛选中的应用。认为差异导向合成在药物研究领域的作用必将变得更加重要。     

Internal/External use of dendrimer in catalysis

Dendrimers, well-defined hyper-branched macromolecules with characteristic globular structures, have inspired chemists and chemical engineers to develop new materials and several applications have been explored. The dendritic molecule has emerged as an attractive material in the field of catalysis and various dendrimer catalysts have been applied not only to catalytic reactions but also to non-catalytic ones such as nanoscale reactor systems. This article presents a review of research work on the dendrimer-based catalysis involving the rational design of homogeneous or heterogeneous chiral dendrimer catalysts for enantioselective reactions and the synthesis of catalytically active bimetallic nanoparticles in the presence of dendrimer as a template. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.