Asymmetric Total Synthesis of Rumphellclovane E

Synthetic Studies of Zoaramine: Construction of the Tetracyclic Skeleton in High Oxidation State

We report herein the synthetic studies toward zoaramine, a member of the family of zoaramine-type marine natural products bearing a unique structure. The major synthetic challenge is the stereoselective construction of the congested tetracyclic [6-6-6-6] skeleton in a high oxidation state. Our key strategies are the following: (1) radical cyclization was designed to install the quaternary stereocenters at C-9, C-22, and C-12 as well as formation of the B and D rings; (2) selective oxidations were realized to introduce the functional groups at C-11 and C-24 by using O2/t-BuOK-promoted hydroxylation and MeReO3-catalyzed Rubottom oxidation. Our studies reveal a special reactivity and stereocontrol model in the specific chemical environments, which might benefit the related synthetic exploration of this family of natural alkaloids.

Total Synthesis of Penicibilaenes Enabled by a Tandem Double Conia-ene Type Reaction

The total syntheses of penicibilaenes A and B are described. The key step is the tBuOK/DMSO-mediated tandem 5-exo-dig Conia-ene type reaction and 6-exo-dig Conia-ene type reaction to install the tricyclic [6.3.1.01,5] dodecane core of penicibilaenes from dibutynyl cyclohexanone in a single step, together with a sequence of copper-mediated conjugate addition and Crabtree's hydrogenation to forge the stereogenic centers at C5 and C2, respectively.

Asymmetric Synthesis of Arboduridine

The first asymmetric total synthesis of the monoterpenoid indole alkaloid arboduridine has been accomplished. The tricyclic A/B/D ring system was constructed by an enantioselective Michael reaction followed by intramolecular nucleophilic addition. Intramolecular α-amination of a ketone forged the piperidine ring, while a Horner-Wadsworth-Emmons (HWE) reaction was used to form the pyrrolidine ring. A reduction cyclization cascade led to formation of the tetrahydrofuran ring.

Marine natural products

Covering: January to December 2021This review covers the literature published in 2021 for marine natural products (MNPs), with 736 citations (724 for the period January to December 2021) 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 (1425 in 416 papers for 2021), 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. An analysis of the number of authors, their affiliations, domestic and international collection locations, focus of MNP studies, citation metrics and journal choices is discussed.

Enantiocontrolled Access to an Intermediate for Highly Functionalized Clovane-Type Terpenoids: Formal Synthesis of Rumphellclovane E

We describe an enantiocontrolled route to a versatile intermediate for the synthesis of highly functionalized clovane-type terpenoids. The synthetic route commenced with (R)-carvone, a commercially available and enantioenriched building block, and an oxygenative strategy was used to concisely access a clovane scaffold. One example of the versatility of the obtained intermediate was the formal synthesis of rumphellclovane E.

Total Synthesis of Clovan-2,9-dione via [3 + 2 + 1] Cycloaddition and Hydroformylation/Aldol Reaction

Here we report the total synthesis of clovan-2,9-dione via Rh-catalyzed [3 + 2 + 1] cycloaddition/hydroformylation/aldol reaction. The [3 + 2 + 1] reaction of 1-yne-vinylcyclopropane and CO was used for the generation of a 5/6 bicyclic skeleton with a bridgehead vinyl group. The hydroformylation reaction converted the congested olefin of the [3 + 2 + 1] cycloadduct to a one-carbon elongated aldehyde, which underwent in situ aldol reaction, with the carbonyl group in the [3 + 2 + 1] cycloadduct, to generate the tricyclic bridged-ring skeleton of the target molecule.

Samarium(ii) iodide-mediated reactions applied to natural product total synthesis

Natural product synthesis remains a field in which new synthetic methods and reagents are continually being evaluated. Due to the demanding structures and complex functionality of many natural products, only powerful and selective methods and reagents will be highlighted in this proceeding. Since its introduction by Henri Kagan, samarium(ii) iodide (SmI2, Kagan's reagent) has found increasing use in chemical synthesis. Over the years, many reviews have been published on the application of SmI2 in numerous reductive coupling procedures as well as in natural product total synthesis. This review highlights recent advances in SmI2-mediated synthetic strategies, as applied in the total synthesis of natural products since 2004.

Total synthesis of remdesivir

Remdesivir, the first drug approved by the FDA to treat COVID-19, is in high demand for patients infected with the SARS-CoV-2 virus. Herein, we report a facile approach minimizing the protecting group manipulations to afford remdesivir in good overall yield.

Expanding Stereoelectronic Limits of endo-tet Cyclizations: Synthesis of Benz[b]azepines from Donor-Acceptor Cyclopropanes

The importance of intramolecular constraints in cyclic transition-state geometries is especially pronounced in n-endo-tet cyclizations, where the usual backside approach of a nucleophile to the breaking bond is impossible for the rings containing less than eight atoms. Herein, we expand the limits of endo-tet cyclizations and show that donor-acceptor cyclopropanes can provide a seven-membered ring via a genuine 6-endo-tet process. Substrates containing a N-alkyl-N-arylcarbamoyl moiety as an acceptor group undergo Lewis acid-induced cyclization to form tetrahydrobenz[b]azepin-2-ones in high yields. The reaction proceeds with the inversion of the configuration at the electrophilic carbon. In this process, a formally six-membered transition state yields a seven-membered ring as the pre-existing cycle is merged into the forming ring. The stereochemistry of the products can be controlled by the reaction time and by the nature of Lewis acid, opening access to both diastereomers by tuning of the reaction conditions.

Asymmetric Total Synthesis of Norzoanthamine

We report herein the asymmetric total synthesis of norzoanthamine using radical reactions as key steps for rapid access to the congested carbocyclic core, which is the major synthetic challenge for most zoanthamine alkaloids. (1) The Ueno-Stork radical cyclization was applied to construct the adjacent quaternary centers at the C-9 and C-22 positions; (2) a Co-catalyzed HAT radical reaction was successfully applied to construct the quaternary center at C-12 via Csp³ -Csp² bond formation; (3) a Mn-catalyzed HAT radical reaction was used to stereospecifically reduce the tetra-substituted olefin (C13=C18) and install the contiguous stereocenters in proximity to the quaternary center. A one-pot bio-inspired cyclization step was finally applied to forge the unstable bis-amino acetal skeleton. Our approach can precisely control the stereochemistry of seven vicinal stereocenters and effectively construct the highly congested heptacyclic skeleton.

Catalytic radical cascade cyclization of alkene-tethered enones to fused bicyclic cyclopropanols

Fused bicyclic cyclopropanols were achieved via an unprecedented HAT-triggered radical cascade reaction of alkene-tethered enones in the presence of an iron catalyst.

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.