Enantioselective Total Synthesis of Macfarlandin C, a Spongian Diterpenoid Harboring a Concave‐Substituted cis ‐Dioxabicyclo[3.3.0]octanone Fragment

Lewis Acid Catalyzed Cyclopropane Ring-Opening-Cyclization Cascade Using Thioureas as a N,N-bisnucleophile: Synthesis of Bicyclic Furo-, Pyrano-, and Pyrrololactams via a Formal [4+1]-Addition

Fused bicyclic cyclopropanes were converted by Lewis acid-catalysis with thioureas to furo-, pyrano, and pyrrololactams with yields of up to 99 % and high diastereoselectivity. The formation of the title compounds, representing a formal [4+1]-cycloaddition to a donor-acceptor substituted cyclopropane, follows a cascade reaction involving SN1-type ring-opening addition and cyclization. Thiourea, being a cost-effective and odorless reagent, acts as an N,N-bis-nucleophile to generate bicyclic compounds containing an N-substituted γ-lactam moiety.

Modern Photocatalytic Strategies in Natural Product Synthesis

Modern photocatalysis has proven its generality for the development and functionalization of native functionalities. To date, the field has found broad applications in diverse research areas, including the total synthesis of natural products. This contribution covers recent reports of total syntheses involving as a key step a photocatalytic reaction. Among the selected examples, the photocatalytic processes proceed in a highly chemo-, regio-, and stereoselective manner, thereby allowing the rapid access to structurally complex architectures under light-driven conditions.

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

Evolution towards green radical generation in total synthesis

The use of radicals as intermediates in total synthesis has evolved since their initial use in the latter half of the twentieth century. Radical generation from metal hydride methodologies has shifted to "greener" techniques including catalytic metal-mediated systems, electrochemical and photoredox-mediated processes. This review will focus on these classical and contemporary methods for radical generation and their applications in recent total syntheses.

Strategic Use of Visible-Light Photoredox Catalysis in Natural Product Synthesis

Recent progress in the development of photocatalytic reactions promoted by visible light is leading to a renaissance in the use of photochemistry in the construction of structurally elaborate organic molecules. Because of the rich functionality found in natural products, studies in natural product total synthesis provide useful insights into functional group compatibility of these new photocatalytic methods as well as their impact on synthetic strategy. In this review, we examine total syntheses published through the end of 2020 that employ a visible-light photoredox catalytic step. To assist someone interested in employing the photocatalytic steps discussed, the review is organized largely by the nature of the bond formed in the photocatalytic step.

Metal-hydride hydrogen atom transfer (MHAT) reactions in natural product synthesis

Functionalization of olefins has been an important transformation in synthetic chemistry. This review will focus on the natural product synthesis employing the MHAT reaction as the key strategy.

General Access to Concave-Substituted cis-Dioxabicyclo[3.3.0]octanones: Enantioselective Total Syntheses of Macfarlandin C and Dendrillolide A

The evolution of a strategy to access the family of rearranged spongian diterpenoids harboring a concave-substituted cis-2,8-dioxabicyclo[3.3.0]octan-3-one fragment is described. The approach involves late-stage fragment coupling of a tertiary-carbon radical and an electron-deficient double bond to form vicinal quaternary and tertiary stereocenters with high fidelity. A stereoselective Mukaiyama hydration is the key step in the subsequent elaboration of the cis-2,8-dioxabicyclo[3.3.0]octan-3-one moiety. This strategy was utilized in enantioselective total syntheses of (-)-macfarlandin C and (+)-dendrillolide A. An efficient construction of enantiopure tetramethyloctahydronaphthalenes was developed during the construction of (-)-macfarlandin C.

Catalytic Hydroxycyclopropanol Ring-Opening Carbonylative Lactonization to Fused Bicyclic Lactones

A novel palladium-catalyzed ring opening carbonylative lactonization of readily available hydroxycyclopropanols was developed to efficiently synthesize tetrahydrofuran (THF) or tetrahydropyran (THP)-fused bicyclic γ-lactones, two privileged scaffolds often found in natural products. The reaction features mild reaction conditions, good functional group tolerability, and scalability. Its application was demonstrated in a short total synthesis of (±)-paeonilide. The fused bicyclic γ-lactone products can be easily diversified to other medicinally important scaffolds, which further broadens the application of this new carbonylation method.