Total Synthesis of (+)-Viridianol, a Marine-Derived Sesquiterpene Embodying the Decahydrocyclobuta[d]indene Framework

Enantioselective Allylboration of Acetylene: A Versatile Tool for the Stereodivergent Synthesis of Natural Products

Efficient catalytic methods that allow the use of simple and abundant chemical feedstocks for the preparation of synthetically versatile compounds are central to modern synthetic chemistry. Acetylene is a basic feedstock with a remarkable production over one million tons per year, although it is underutilized in the stereoselective synthesis of fine chemicals. Here we report a facile catalytic multicomponent reaction that allows for the enantio- and diastereoselective allylboration of acetylene gas. This process is catalyzed by a chiral copper catalyst, operates without specialized equipment or pressurization, and provides chiral skipped dienes bearing stereodefined and orthogonally functionalized olefins with excellent levels of chemo-, regio-, enantio- and diastereoselectivity. The combined stereochemical features and orthogonal functionalization make the products privileged structural scaffolds to access the complete set of stereoisomers of the chiral skipped diene core through simple enantio- and diastereodivergent pathways. The utility of the method is demonstrated with the enantioselective synthesis of three bioactive natural skipped diene products, namely (+)-Nyasol, (+)-Hinokiresinol and Phorbasin C, and other related synthetically relevant chiral molecules.

Marine natural products

This review covers the literature published between January and December in 2018 for marine natural products (MNPs), with 717 citations (706 for the period January to December 2018) 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 (1554 in 469 papers for 2018), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. The proportion of MNPs assigned absolute configuration over the last decade is also surveyed.

The Synthesis, Structural Characterisation, and Chemoselective Manipulation of Certain Functionalised Cyclic Sulfates Derived from Chiral, Non-Racemic, and Polysubstituted Bicyclo[2.2.2]octane-2,3-diols

Certain cyclic sulfates (e.g. 23) together with various of their precursor sulfites (e.g. 21 and 22) have been prepared from the corresponding chiral, non-racemic bicyclo[2.2.2]octane-2,3-diols (e.g. 20). Such diols are obtained by engaging the corresponding enzymatically derived and enantiomerically enriched or homochiral cis-1,2-dihydrocatechol (e.g. 10) or certain derivatives in either inter- or intra-molecular Diels–Alder cycloaddition reactions. Other functionalities present within the title compounds can be chemoselectively manipulated without adversely affecting the associated sulfate residues.

Syntheses of Dimethyl (1S,2R)-3-Bromocyclohexa-3,5-diene-1,2-dicarboxylate and Its Enantiomer

The title compounds, (-)-2 and (+)-2, representing potentially valuable building blocks for chemical synthesis, have each been prepared from cyclopentanone in eight steps. The pivotal one involves a resolution, through the quinine- or quinidine-promoted methanolysis of the cyclic anhydride (±)-10, leading to chromatographically separable pairs of enantiomerically pure forms of regioisomeric methyl half esters.

The Application of Dioxygenase-Based Chemoenzymatic Processes to the Total Synthesis of Natural Products

This Minireview describes the exploitation of certain enzymatically derived, readily accessible, and enantiomerically pure cis-1,2-dihydrocatechols as starting materials in the chemical synthesis of a range of biologically active natural products, most notably sesquiterpenoids and alkaloids.

Chemoenzymatic Synthesis of (-)-Ribisins A and B from Dibenzo[b,d]furan

cis-Dihydrodiols, derived from monocyclic aromatic compounds, are valuable chiral pool intermediates for the synthesis of cyclic natural products. A drawback of this approach, to the synthesis of polycyclic secondary metabolites, is that additional rings must be annulated. To date, relatively few chiral natural products have been synthesized from polycyclic arene cis-dihydrodiols. Fungal metabolites, (-)-ribisins A and B, have now been obtained by functional group manipulation of a tricyclic arene metabolite, obtained from toluene dioxygenase-catalyzed regioselective and stereoselective cis-dihydroxylations of dibenzo[b,d]furan. The synthetic sequences were marginally shorter than the alternative routes, using monocyclic arene cis-dihydrodiols, and required no carbon-carbon bond-forming reactions.

Synthetic Studies on the Marine-Derived Sesquiterpene (+)-Viridianol: Divergent Behaviour of Two Structurally Related, Ring-Fused Cyclopropanes Under the Same Hydrogenolytic Conditions

Hydrogenolytic cleavage of the ring-fused cyclopropane 11 using hydrogen in the presence of platinum oxide afforded the gem-dimethylated cyclohexane 12 in 99% yield. In contrast, analogous treatment of congener 13 afforded only trace amounts of the targeted and gem-dimethylated sesquiterpene (+)-viridianol (1), the major products of reaction now being the vic-dimethylated compound 14 and the 2-fold ring-cleavage product 15.

Benefits of Unconventional Methods in the Total Synthesis of Natural Products

This article provides a survey of four "unconventional" methods employed in the synthesis of natural products in the Hudlicky group. The utility of flash vacuum pyrolysis is highlighted by examples of many natural products attained via vinylcyclopropane-cyclopentene rearrangement and its heterocyclic variants. Preparative organic electrochemistry was used in oxidations and reductions with levels of selectivity unattainable by conventional methods. Yeast reduction of ketoesters was featured in the total synthesis of pyrrolizidine alkaloids. Finally, the use of toluene dioxygenase-mediated dihydroxylations in enantioselective synthesis of natural products concludes this presentation. Recently, synthesized targets in the period 2010-2019 are listed in the accompanying table. The results of research from the Hudlicky group are placed in appropriate context with the work of others, and a detailed guide to the current literature is provided.