Catalysis of Cascade and Multicomponent Reactions of Carbonyl Compounds and CH Acids by Electricity

This review is concerned with modern trends in the use of electrochemically induced chain reactions in cascade and multicomponent electroorganic synthesis. The review summarizes the data on the use of electrochemically induced chain reactions in cascade and multicomponent organic synthesis, which were published mainly in the last decade.     

Cascade Syntheses Routes to the Centrocountins

Cascade and domino reactions that proceed through multiple steps in one pot and include multiple bond formations are promising methods for the rapid and efficient generation of complex molecular architectures, including the scaffolds of classes of complex natural product. We describe the development of various one‐pot cascade reaction sequences to yield centrocountins, which are tetracyclic indole derivatives with the basic scaffold of numerous polycyclic alkaloids. The mechanistic investigation of a sequence employing readily available alkynes and 3‐formylchromones as starting materials provided evidence that this one‐pot synthesis proceeds through at least twelve consecutive transformations and includes at least nine different chemical reactions, making it the longest cascade reaction sequence known to date. We describe the scope and limitations of the cascade synthesis approaches and the development of an enantioselectively catalyzed centrocountin synthesis.     

Bioinspired Synthesis of (+)‐Cinchonidine Using Cascade Reactions

The development of efficient syntheses of complex natural products has long been a major challenge in synthetic chemistry. Designing cascade reactions and employing bioinspired transformations are an important and reliable means of achieving this goal. Presented here is a combination of these two strategies, which allow efficient asymmetric synthesis of the cinchona alkaloid (+)‐cinchonidine. The key steps of this synthesis are a controllable, visible‐light‐induced photoredox radical cascade reaction to efficiently access the tetracyclic monoterpenoid indole alkaloid core, as well as a practical biomimetic cascade rearrangement for the indole to quinoline transformation. The use of stereoselective chemical transformations in this work makes it an efficient synthesis of (+)‐cinchonidine.     

炔醇分子内环化促发的串联反应在螺杂环化合物合成中的应用

螺杂环化合物独特的立体结构和丰富的理化特性,激发了研究工作者对其高效合成方法的持续关注.炔醇在过渡金属作用下经exo-dig式分子内环化可原位形成环外烯醇醚.其作为一类高活性的C2合成子,能够与同时具有亲电和亲核特性的“双亲性底物”发生串联反应,实现螺杂环骨架的快速构建.综述了近年来炔醇分子内环化促发的串联反应在螺杂环化合物合成中的应用进展,以期激发更多相关研究工作的设计与报道.按照参与螺环构建的“双亲性底物”原子数目的不同进行分类,重点阐述了反应采用的催化体系和反应机制,分析了目前该领域存在的挑战,并对未来的发展进行了展望.     

二芳基脯氨醇衍生物催化的硝基烯参与的多组分不对称串联合成研究进展

硝基烯是一类重要的有机合成子,以硝基烯烃为原料,二芳基脯氨醇衍生物催化的多组分不对称串联反应是构建复杂手性化合物的重要方法,被广泛应用于有机合成和新药开发领域.根据构建的目标化合物类型,较全面地总结了基于二芳基脯氨醇衍生物催化、硝基烯为合成子的多组分不对称串联反应的合成研究,从反应的催化剂体系、反应机理、实验结果、反应优点、存在的问题和局限性等方面进行介绍,并对今后的发展做出展望.     

A Short Synthesis of (±)-Matrine

Three different radical reactions were used in a short total synthesis of (±)-matrine ( 1 ). Two of the four six-membered rings and four new bonds were created in one radical cascade involving intermolecular addition followed by two successive cyclizations and transfer of a xanthate group.     

Energochemical technologies: energy and bulk/basic chemicals in a single process

The exoergic reactions, which underlie the production of large-scale basic chemicals for organic industry, can be used for one-pot generation of energy and chemical products. Typical examples include methane oxidative conversion to produce synthesis gas and methane oxidative dimerization to give ethylene and ethane.     

Cascade Reactions: A Driving Force in Akuammiline Alkaloid Total Synthesis

The akuammiline alkaloids are a family of intricate natural products which have received considerable attention from scientists worldwide. Despite the fact that many members of this alkaloid class were discovered over 50 years ago, synthetic chemistry has been unable to address their architectures until recently. This minireview provides a brief overview of the rich history of the akuammiline alkaloids, including their isolation, structural features, biological activity, and proposed biosyntheses. Furthermore, several recently completed total syntheses are discussed in detail. These examples not only serve to highlight modern achievements in alkaloid total synthesis, but also demonstrate how the molecular scaffolds of the akuammilines have provided inspiration for the discovery and implementation of innovative cascade reactions for the rapid assembly of complex structures.     

The Cascade Reactions of Indigo with Propargyl Substrates for Heterocyclic and Photophysical Diversity

The synthesis of structurally diverse heterocycles for chemical space exploration was achieved via the cascade reactions of indigo with propargylic electrophiles. New pyrazinodiindolodione, naphthyridinedione, azepinodiindolone, oxazinoindolone and pyrrolodione products were prepared in one pot reactions by varying the leaving group (-Cl, -Br, -OMs, -OTs) or propargyl terminal functionality (-H, -Me, -Ph, -Ar). Mechanistic and density functional theory studies revealed that the unsaturated propargyl moiety can behave as an electrophile when aromatic terminal substitutions are made, and therefore competes with leaving group substitution for new outcomes. Selected products from the cascade reactions were investigated for their absorption and fluorescence properties, including transient absorption spectroscopy. This revealed polarity dependent excited state relaxation pathways, fluorescence, and triplet formation, thus highlighting these reactions as a means to access diverse functional materials rapidly.     

Biomimetic Total Synthesis of (±)-Homodimericin A

A biomimetic total synthesis of racemic homodimericin A was achieved in seven steps, including two cascade reactions. Aqueous buffer solutions are found to help both the oxidative dimerization cascade and the intramolecular Diels–Alder cascade. This synthetic sequence validates key steps in the biogenetic proposal of homodimericin A.     

Organocatalyzed tandem process involving asymmetric protonations as a stereo-defining step

Enantioselective protonation reactions of enolates, enols, enol ethers, or enol esters have been extensively studied. On the other hand, their applications in tandem or cascade sequence have not been fully explored and examples of such reactions employing organocatalysts are few. This account describes some of the most common synthetic strategies recently developed to address such challenge.     

Facile and regioselective synthesis of functionalized benzenes via cascade reactions of 1,2-allenic ketones with 4-sulfonyl crotonates

An efficient and regioselective synthesis of functionalized benzenes via the cascade reactions of 1,2-allenic ketones with 4-sulfonyl crotonates under mild reaction conditions has been established. Mechanistically, the formation of the title compounds involves a cascade procedure consisting of an intermolecular regioselective Michael addition followed by an intramolecular condensation and aromatization. Compared with those of α,β-unsaturated aldehydes/ketones, the reactions of 1,2-allenic ketones with 4-sulfonyl crotonates demonstrated contrary regio-selectivity and distinct reaction conditions. Moreover, the functionalized benzene products obtained herein were found to be ready intermediates for the synthesis of fluorenone and anthracenone derivatives.     

A Regio‐ and Stereoselective ω‐Transaminase/Monoamine Oxidase Cascade for the Synthesis of Chiral 2,5‐Disubstituted Pyrrolidines

Biocatalytic approaches to the synthesis of optically pure chiral amines, starting from simple achiral building blocks, are highly desirable because such motifs are present in a wide variety of important natural products and pharmaceutical compounds. Herein, a novel one‐pot ω‐transaminase (TA)/monoamine oxidase (MAO‐N) cascade process for the synthesis of chiral 2,5‐disubstituted pyrrolidines is reported. The reactions proceeded with excellent enantio‐ and diastereoselectivity (>94 % ee; >98 % de) and can be performed on a preparative scale. This methodology exploits the complementary regio‐ and stereoselectivity displayed by both enzymes, which ensures that the stereogenic center established by the transaminase is not affected by the monoamine oxidase, and highlights the potential of this multienzyme cascade for the efficient synthesis of chiral building blocks.     

De Novo and Divergent Synthesis of Highly Functionalized Furans by Cascade Reactions of 2-Hydroxy-1,4-diones with Nucleophiles

Herein, a divergent synthesis of a variety of 2α- and 5α-substituted furan derivatives from 2-hydroxy-1,4-diones is reported. By using appropriate substrates and an acid catalyst, the reactions occurred selectively through cyclization/1,6-conjugate addition or cyclization/Friedel–Crafts-type cascade reactions. A broad range of nucleophilic reagents (>10 types for the 1,6-conjugate addition for 5α substitution and >20 types for the Friedel–Crafts-type cascade reaction for 2α substitution), including alcohols, amides, furan, thiophene, pyrrole, indole, phenols, and many others, can successfully participate in the reactions, providing a universal strategy for a diversity-oriented synthesis of α-substituted furan derivatives. Deuteriation experiments and DFT calculations were carried out to support the proposed reaction mechanisms. Antifungal activity experiments revealed that products with an indole or 4-hydroxycoumarin core substituted at the 2α position showed moderate activities against Rhizoctorzia solani and Botrytis cinerea, respectively.     

Studies toward brevisulcenal F via convergent strategies for marine ladder polyether synthesis

Shortly after the initial isolation of marine ladder polyether natural products, biomimetic epoxide-opening cascade reactions were proposed as an efficient strategy for the synthesis of these compounds. However, difficulties in assembling the cascade precursors have limited the realization of these cascades. In this report, we describe strategies that provide convergent access to cascade precursors via regioselective allylation and efficient fragment coupling. We then investigate epoxide-opening cascades promoted by strong bases for the formation of fused tetrahydropyrans. These strategies are evaluated in the context of the synthesis of rings CDEFG of brevisulcenal F.     

Recent Advances in Transition‐Metal‐Free Oxygenation of Alkene C=C Double Bonds for Carbonyl Generation

Carbonyl‐forming reactions are a class of fundamental transformations in organic chemistry. Guided by the current importance of environmentally benign metal‐free catalysis and synthesis, herein we review recent advances in carbonyl‐generation reactions based on alkene C=C double oxygenation as well as related cascade reactions in the synthesis of diverse organic products. The content of this focus review consists of two important but different reaction models: oxygenation based on full C=C double‐bond cleavage and oxygenation based on partial C=C double‐bond cleavage.     

Intercepted Decarboxylative Allylations of Nitroalkanoates

Using palladium-catalyzed decarboxylation, several cascade reactions of allyl and prenyl nitroalkanoates that lead to nitro-containing chemical building blocks are described. A nitronate Michael addition/Tsuji-Trost allylation cascade was developed, leading to functionally dense chemical building blocks. Likewise, a Tsuji-Trost/decarboxylative protonation sequence was developed for the synthesis of orthogonally functionalized 2° nitroalkanes. The latter method provides rapid access to the indolizidine core.     

A Cascade Synthesis of Aminohydantoins Using In Situ‐Generated N‐Substituted Isocyanates

Nitrogen‐substituted isocyanates are rarely utilized but powerful building blocks for the development of cascade reactions in heterocyclic synthesis. These reactive amphoteric intermediates can be accessed in situ via an equilibrium that allows controlled reactivity in the presence of bifunctional partners such as α‐amino esters. A cascade reaction has been carried out that forms 3‐aminohydantoin derivatives using simple phenoxycarbonyl derivatives of hydrazides and hydrazones as precursors of N‐substituted‐isocyanates. This method allows rapid assembly of complex aminohydantoin derivatives, including analogues of medicinally‐relevant compounds, using simple reactants.     

Bifunctional solid catalysts for chemoselective hydrogenation-cyclisation-amination cascade reactions of relevance for the synthesis of pharmaceuticals

The benzodiazepines olanzapine and clozapine are nowadays manufactured by a three-step process with a final yield below 50%. An approach to environmentally-friendly intensive processes consists in the development of multifunctional solid catalyst able to catalyze multistep reactions. Here, a bifunctional metal-acid solid catalyst has been prepared and is able to carry out hydrogenation-cyclisation-amination reactions in a cascade process. The catalytic system is illustrated for the synthesis of these important antipsychotics, being an alternative for the current industrial process that requires three steps batch reactions, using mineral acids and bases, and stoichiometric amounts of SnCl₂.     

Multifaceted Behavior of 2-Cyanobenzaldehyde and 2-Acylbenzonitriles in the Synthesis of Isoindolinones,Phthalides and Related Heterocycles

2-Cyanobenzaldehye (also called 2-formylbenzonitrile) and related 2-acylbenzonitriles belong to a class of bifunctional aromatic compounds that emerged as useful starting materials in developing efficient cascade-type reactions leading to different heterocyclic compounds. The variety of sometimes unpredictable mechanisms that rise from these structurally simple starting materials renders this class of compounds unique to afford, through divergent cascade reactions, heterocycles like isoindolinones, phthalides (also known with the name of isobenzofuranones), imidates, and in less extent isoindolin-1-imine, six- and seven-membered heterocycles, porphyrins, also in asymmetric way exploiting different organocatalytic activation modes. To give a picture, this chemistry can be associated to Goldberg variations which stem from a common motive in a pressing and surprising way. In this Review, emphasis is also given to the synthetic methods for the access to substituted 2-cyanobenzaldehydes and 2-acylbenzonitriles which allowed to enlarge the scope of the described cascade reactions.