Total Synthesis of Repraesentin F and Configuration Reassignment by a Gold(I)-Catalyzed Cyclization Cascade

Gold-catalyzed cyclization and cycloaddition in natural product synthesis

Covering: 2016 to mid 2023Transition metal catalysis, known for its remarkable capacity to expedite the assembly of molecular complexity from readily available starting materials in a single operation, occupies a central position in contemporary chemical synthesis. Within this landscape, gold-catalyzed reactions present a novel and versatile paradigm, offering robust frameworks for accessing diverse structural motifs. In this review, we highlighted a curated selection of publications in the past 8 years, focusing on the deployment of homogeneous gold catalysis in the ring-forming step for the total synthesis of natural products. These investigations are categorized based on the specific ring formations they engender, accentuating the prevailing gold-catalyzed methodologies applied to surmount intricate challenges in natural products synthesis.

Interrupted Furan-Yne Cyclization: Access to Unsaturated Dicarbonyl Compounds and Their Subsequent Transformation into Functionalized Pyridazines

The key carbenoid intermediate of transition-metal-catalyzed furan-yne cyclization in Hashmi phenol synthesis could be efficiently intercepted with water under the developed reaction conditions in order to provide access to functionalized unsaturated dicarbonyl compounds that might serve as convenient precursors for the straightforward synthesis of annulated pyridazines.

Simmons-Smith Cyclopropanation: A Multifaceted Synthetic Protocol toward the Synthesis of Natural Products and Drugs: A Review

Simmons-Smith cyclopropanation is a widely used reaction in organic synthesis for stereospecific conversion of alkenes into cyclopropane. The utility of this reaction can be realized by the fact that the cyclopropane motif is a privileged synthetic intermediate and a core structural unit of many biologically active natural compounds such as terpenoids, alkaloids, nucleosides, amino acids, fatty acids, polyketides and drugs. The modified form of Simmons-Smith cyclopropanation involves the employment of Et2Zn and CH2I2 (Furukawa reagent) toward the total synthesis of a variety of structurally complex natural products that possess broad range of biological activities including anticancer, antimicrobial and antiviral activities. This review aims to provide an intriguing glimpse of the Furukawa-modified Simmons-Smith cyclopropanation, within the year range of 2005 to 2022.

Recent progress in the homogeneous gold-catalysed cycloisomerisation reactions

This review focuses on recent advancements in the efficacy of gold catalysts for the cycloisomerisation of ynamides, diynes, and 1,n-enynes to build complex molecules, with critical insight into their mechanism and reaction scope.

Iron‐Catalyzed Cycloisomerization and C−C Bond Activation to Access Non‐canonical Tricyclic Cyclobutanes

Cycloisomerizations are powerful skeletal rearrangements that allow the construction of complex molecular architectures in an atom‐economic way. We present here an unusual type of cyclopropyl enyne cycloisomerization that couples the process of a cycloisomerization with the activation of a C−C bond in cyclopropanes. A set of substituted non‐canonical tricyclic cyclobutanes were synthesized under mild conditions using [(Ph₃P)₂Fe(CO)(NO)]BF₄ as catalyst in good to excellent yields with high levels of stereocontrol.

Gold-Catalysed Rearrangement of Unconventional Cyclopropane-Tethered 1,5-Enynes

The synthesis of particular cyclopropane-tethered 1,5-enynes, namely 6-alkynyl-4-alkylidenebicyclo[3.1.0]hex-2-enes, enabled the discovery of an unprecedented gold-catalyzed rearrangment to indenes. A computational study of the mechanism of this profund skeleton rearrangement is...

Gold Catalysis Enabling Furan-Fused Cyclobutenes as a Platform toward Cross Cycloadditions

The inherently strained furan-fused cyclobutenes, in situ generated via cycloisomerizations of allenyl ketones bearing cyclopropyl moiety under gold catalysis, have been utilized as reactive building blocks toward cross cycloadditions. The [4 + 2] and [3 + 2] annulations of these species with benzo[c]isoxazoles and N-iminoquinazolinium ylides furnish various three-dimensional cyclobutane-bridged polyheterocycles in good yields. A wide range of typically electron-deficient 1,3-dienes, heterodienes, and 1,3-dipoles can trap furan-fused cyclobutenes to afford several polycyclic architectures.

The Total Synthesis of Diquinane-Containing Natural Products

Diquinane or bicyclo[3.3.0]octane is a conspicuous structural unit existing in the carbo-frameworks of a wide range of natural products such as alkaloids and terpenoids. These diquinane-containing molecules not merely exhibit intriguing architectures, but also showcase a broad spectrum of significant bioactivities, which draw widespread attention from the global synthetic community. During the past decade, with an aim to accomplish the total syntheses of such specified cornucopias of natural products, a variety of elegant strategies for construction of the diquinane ring system have been disclosed. In this Minireview, the achievements on this subject in the timeline from 2010 to June 2020 are demonstrated and it is discussed how the diquinane unit is strategically forged in the context of the specific target structure. In addition, impacts of the selected works to the field of natural product total synthesis is highlighted and the particular outlook of diquinane-containing natural product synthesis is provided.

Gold-Catalyzed Synthesis of Small Rings

Three- and four-membered rings, widespread motifs in nature and medicinal chemistry, have fascinated chemists ever since their discovery. However, due to energetic considerations, small rings are often difficult to assemble. In this regard, homogeneous gold catalysis has emerged as a powerful tool to construct these highly strained carbocycles. This review aims to provide a comprehensive summary of all the major advances and discoveries made in the gold-catalyzed synthesis of cyclopropanes, cyclopropenes, cyclobutanes, cyclobutenes, and their corresponding heterocyclic or heterosubstituted analogs.

Gold-Catalyzed Synthetic Strategies towards Four-Carbon Ring Systems

Four carbon ring systems are frequently present in natural products with remarkable biological activities such as terpenoids, alkaloids, and steroids. The development of new strategies for the assembly of these structures in a rapid and efficient manner has attracted the interest of synthetic chemists for a long time. The current research is focused mainly on the development of synthetic methods that can be performed under mild reaction conditions with a high tolerance to functional groups. In recent years, gold complexes have turned into excellent candidates for this aim, owing to their high reactivity, and are thus capable of promoting a wide range of transformations under mild conditions. Their remarkable efficiency has been thoroughly demonstrated in the synthesis of complex organic molecules from simple starting materials. This review summarizes the main synthetic strategies described for gold-catalyzed four-carbon ring formation, as well as their application in the synthesis of natural products.

General Synthesis of Cyclopropanols via Organometallic Addition to 1-Sulfonylcyclopropanols as Cyclopropanone Precursors

The addition of organometallic reagents to ketones constitutes one of the most straightforward synthetic approaches to tertiary alcohols. However, due to the absence of a well-behaved class of cyclopropanone surrogates accessible in enantioenriched form, such a trivial synthetic disconnection has received very little attention in the literature for the formation of tertiary cyclopropanols. In this work, we report a simple and high-yielding synthesis of 1-substituted cyclopropanols via the addition of diverse organometallic reagents to 1-phenylsulfonylcyclopropanols, acting here as in situ precursors of the corresponding cyclopropanones. The transformation is shown to be amenable to sp-, sp²-, or sp³-hybridized organometallic C-nucleophiles under mild conditions, and the use of enantioenriched substrates led to highly diastereoselective additions and the formation of optically active cyclopropanols.

Ring-fused cyclobutanes via cycloisomerization of alkylidenecyclopropane acylsilanes

A novel Lewis acid-catalyzed cycloisomerization of alkylidenecyclopropane acylsilanes is disclosed. The readily available starting materials participate in tandem Prins addition/ring expansion/1,2-silyl shift to grant access to bicyclo[4.2.0]octanes and bicyclo[3.2.0]heptanes, which are common motifs in terpenoid natural products. Notably, the transformation relies on the ability of acylsilanes to act sequentially as acceptors and donors on the same carbon atom.

A novel Lewis acid-catalyzed cycloisomerization of alkylidenecyclopropane acylsilanes is disclosed that involves tandem Prins addition/ring expansion/1,2-silyl shift to grant access to bicyclo[4.2.0]octanes and bicyclo[3.2.0]heptanes.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

The screening and testing of extracts against a variety of pharmacological targets in order to benefit from the immense natural chemical diversity is a concern in many laboratories worldwide. And several successes have been recorded in finding new actives in natural products, some of which have become new drugs or new sources of inspiration for drugs. But in view of the vast amount of research on the subject, it is surprising that not more drug candidates were found. In our view, it is fundamental to reflect upon the approaches of such drug discovery programs and the technical processes that are used, along with their inherent difficulties and biases. Based on an extensive survey of recent publications, we discuss the origin and the variety of natural chemical diversity as well as the strategies to having the potential to embrace this diversity. It seemed to us that some of the difficulties of the area could be related with the technical approaches that are used, so the present review begins with synthetizing some of the more used discovery strategies, exemplifying some key points, in order to address some of their limitations. It appears that one of the challenges of natural product-based drug discovery programs should be an easier access to renewable sources of plant-derived products. Maximizing the use of the data together with the exploration of chemical diversity while working on reasonable supply of natural product-based entities could be a way to answer this challenge. We suggested alternative ways to access and explore part of this chemical diversity with in vitro cultures. We also reinforced how important it was organizing and making available this worldwide knowledge in an "inventory" of natural products and their sources. And finally, we focused on strategies based on synthetic biology and syntheses that allow reaching industrial scale supply. Approaches based on the opportunities lying in untapped natural plant chemical diversity are also considered.

Coligand driven diverse organometallation in benzothiazolyl-hydrazone derivatized pyrene: ortho vs. peri C–H activation

Divergent aromatic C–H activation at both ortho and peri positions in polyaromatic hydrocarbons has been successfully accomplished by suitable variation of the coligand.

Recent advances in the total synthesis of cyclobutane-containing natural products

Recent developments of strategies on the construction of cyclobutanes and their application in complex natural product synthesis are discussed.

Gold-Catalyzed Homogeneous (Cyclo)Isomerization Reactions

Gold is currently one of the most used metals in organometallic catalysis. The ability of gold to activate unsaturated groups in different modes, together with its tolerance to a wide range of functional groups and reaction conditions, turns gold-based complexes into efficient and highly sought after catalysts. Natural products and relevant compounds with biological and pharmaceutical activity are often characterized by complex molecular structures. (Cyclo)isomerization reactions are often a useful strategy for the generation of this molecular complexity from synthetically accessible reactants. In this review, we collect the most recent contributions in which gold(I)- and/or gold(III)-catalysts mediate intramolecular (cyclo)isomerization transformations of unsaturated species, which commonly feature allene or alkyne motifs, and organize them depending on the substrate and the reaction type.

Twelve-Step Asymmetric Synthesis of (-)-Nodulisporic Acid C

A short, enantioselective synthesis of (-)-nodulisporic acid C is described. The route features two highly diastereoselective polycyclizations en route to the terpenoid core and the indenopyran fragment and a highly convergent assembly of a challenging indole moiety. Application of this chemistry allows for a 12-step synthesis of the target indoloterpenoid from commercially available material.