Total Syntheses of All the Amathaspiramides

Gold(I)-catalysed cyclisation of (E)-ketene-N,O-acetals: a synthetic route toward spiro-oxazole-γ-lactones

In this study, we developed a cascade 5,5-cyclisation of internal ketene-N,O-acetals utilizing homogeneous Au(I) catalysis. This process involves an initial 5-exo-dig carbocyclisation, followed by a 5-exo-dig heterocyclisation that stereoselectively incorporates the O-atom of a water molecule into an N-tethered propargyl alkyne. This sequential reaction results in the formation of one C-C, two C-O, and two C-I bonds, ultimately leading to the synthesis of spiro-α-iodo-γ-lactone structures featuring oxazole rings in good yields.

Stereodivergent synthesis of α-fluoro α-azaaryl γ-butyrolactones via cooperative copper and iridium catalysis

The development of stereodivergent synthetic methods to access all four stereoisomers of biologically important α-fluoro γ-butyrolactones containing vicinal stereocenters is of great importance and poses a formidable challenge owing to ring strain and steric hindrance. Herein, a novel asymmetric [3+2] annulation of α-fluoro α-azaaryl acetates with vinylethylene carbonate was successfully developed through Cu/Ir-catalyzed cascade allylic alkylation/lactonization, affording a variety of enantioenriched α-fluoro γ-butyrolactones bearing vicinal stereogenic centers with high reaction efficiency and excellent levels of both stereoselectivity and regioselectivity (up to 98% yield, generally >20:1 dr and >99% ee). Notably, all four stereoisomers of these pharmaceutically valuable molecules could be accessed individually via simple permutations of two enantiomeric catalysts. In addition, other azaaryl acetates bearing α-methyl, α-chlorine or α-phenyl group were tolerated well in this transformation. Reaction mechanistic investigations were conducted to explore the process of this bimetallic catalysis based on the results of reaction intermediates, isotopic labelling experiments, and kinetic studies.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

exo'-Selective Construction of Spirobipyrrolidines by the Silver-catalyzed Asymmetric [3+2] Cycloaddition of Imino Esters with 4-Benzylidene-2,3-dioxopyrrolidines

The unprecedented Ag-catalyzed exo ' -selective [3+2] cycloaddition of imino esters with 4-benzylidene-2,3-dioxopyrrolidines is described. The reaction was efficiently catalyzed by AgOAc/( R , S p )-ThioClickFerrophos (TCF) leading to the construction of the corresponding spirobipyrrolidine scaffolds in excellent enantio- and diastereoselectivities. This reaction is the first example of a silver-catalyzed exo ' -selective asymmetric [3+2] cycloaddition, as well as the first exo ' -selective spirobipyrrolidine construction via a [3+2] cycloaddition process using imino esters. The wide substrate scope of this reaction enabled the preparation of structurally diverse spirobipyrrolidine derivatives, which are attracting attention as targets for drug discovery. Mechanistic studies suggested that the unusual exo ' -selectivity of this reaction is not due to epimerization following the common exo - or endo -selective cycloaddition, but instead is due to a stepwise Michael addition/Mannich sequence with bond rotation.

Total Synthesis of (-)-Amathaspiramide A via One-pot Aldol Addition/Transamidification Reaction

The total synthesis of (-)-amathaspiramide A was accomplished through an efficient construction of chiral aza-spirobicyclic core by aldol addition/transamidification cascade. The scope of the efficient construction methodology was investigated. Configuration...

Stereodivergent Synthesis of Enantioenriched γ-Butyrolactones Bearing Two Vicinal Stereocenters Enabled by Synergistic Copper and Iridium Catalysis

By virtue of a fundamentally new reaction model of azomethine ylide serving as a two-atom synthon, we present the first example of stereodivergent preparation of γ-butyrolactones via synergistic Cu/Ir-catalyzed asymmetric cascade allylation/lactonization, and all four stereoisomers of γ-butyrolactones bearing two vicinal stereocenters are accessible with excellent diastereoselective and enantioselective control. The chiral Ir^III -π-allyl intermediate was separated and characterized to understand the origin of the regio- and stereoselectivity of the initial C-C bond formation process. Control experiments shed some light on the catalyst/substrate and catalyst/catalyst interactions in this dual catalytic system to rationalize the related kinetic/dynamic kinetic resolution process with different catalyst combinations. The enantioenriched γ-butyrolactone products were converted into an array of structurally complex chiral molecules and organocatalysts that were otherwise inaccessible.

The Phylum Bryozoa: From Biology to Biomedical Potential

Less than one percent of marine natural products characterized since 1963 have been obtained from the phylum Bryozoa which, therefore, still represents a huge reservoir for the discovery of bioactive metabolites with its ~6000 described species. The current review is designed to highlight how bryozoans use sophisticated chemical defenses against their numerous predators and competitors, and which can be harbored for medicinal uses. This review collates all currently available chemoecological data about bryozoans and lists potential applications/benefits for human health. The core of the current review relates to the potential of bryozoan metabolites in human diseases with particular attention to viral, brain, and parasitic diseases. It additionally weighs the pros and cons of total syntheses of some bryozoan metabolites versus the synthesis of non-natural analogues, and explores the hopes put into the development of biotechnological approaches to provide sustainable amounts of bryozoan metabolites without harming the natural environment.

Asymmetric Cα-Alkylation of Proline via Chirality Transfers of Conformationally Restricted Proline Derivative: Application to the Total Synthesis of (-)-Amathaspiramide F

An efficient strategy for the asymmetric synthesis of Cα-tetrasubstituted proline derivatives from proline has been established. A nitrogen-fused bicyclic system was devised to control the stereodynamics of proline. Through N-quaternizations with allylic electrophiles followed by [2,3]-rearrangements, the bicyclic proline system delivered enantioenriched Cα-tetrasubstituted prolines. This strategy was applied to the concise total synthesis of (-)-amathaspiramide F.

Calcium(ii)-catalyzed enantioselective conjugate additions of amines

The direct enantioselective chiral calcium(ii)·phosphate complex (Ca[CPA]₂)-catalyzed conjugate addition of unprotected alkyl amines to maleimides was developed.

The direct enantioselective chiral calcium(ii)·phosphate complex (Ca[CPA]₂)-catalyzed conjugate addition of unprotected alkyl amines to maleimides was developed. This mild catalytic system represents a significant advance towards the general convergent asymmetric amination of α,β-unsaturated electrophiles, providing medicinally relevant chiral aminosuccinimide products in high yields and enantioselectivities. Furthermore, the catalyst can be reused directly from a previously chromatographed reaction and still maintain both high yield and selectivity.

Phosphine-catalyzed [3 + 2] annulation reaction: highly regio- and diastereoselective synthesis of 2-azaspiro[4.4]nonene-1,3-diones

A novel method for phosphine-catalyzed [3 + 2] annulation of γ-substituted allenoates with succinimides was developed, which was successfully applied to the synthesis of 2-azaspiro[4.4]nonene-1,3-diones derivatives in 50–96% yield, with high regio- and diastereoselectivities.

A Synthesis of Exiguaquinol Dessulfate

A concise and stereoselective synthesis of exiguaquinol dessulfate is described. Sequential application of a Diels-Alder cycloaddition, a desymmetrizing aldol addition, and a reductive Heck cyclization established most of the architecture of exiguaquinol, and a carefully choreographed introduction of the polar substituents afforded the title compound; unfortunately, naphthoquinol sulfation could not be achieved to deliver exiguaquinol. Our hypothesis regarding the configurational preference of the N-acyl hemiaminal, which was based upon an analysis of internal hydrogen-bonding interactions with polar functional groups, was proven correct. A late-stage intermediate did not demonstrate bactericidal activity against H. pylori cultures.

Synthetic approaches towards alkaloids bearing α-tertiary amines

Alkaloids account for some of the most beautiful and biologically active natural products. Although they are usually classified along biosynthetic criteria, they can also be categorized according to certain structural motifs. Amongst these, the α-tertiary amine (ATA), i.e. a tetrasubstituted carbon atom surrounded by three carbons and one nitrogen, is particularly interesting. A limited number of methods have been described to access this functional group and fewer still are commonly used in synthesis. Herein, we review some approaches to asymmetrically access ATAs and provide an overview of alkaloid total syntheses where those have been employed.

Radical-mediated dehydrative preparation of cyclic imides using (NH4)2S2O8-DMSO: application to the synthesis of vernakalant

Ammonium persulfate–dimethyl sulfoxide (APS–DMSO) has been developed as an efficient and new dehydrating reagent for a convenient one-pot process for the synthesis of miscellaneous cyclic imides in high yields starting from readily available primary amines and cyclic anhydrides. A plausible radical mechanism involving DMSO has been proposed. The application of this facile one-pot imide forming process has been demonstrated for a practical synthesis of vernakalant.

Recent Applications and Developments of Organic Azides in Total Synthesis of Natural Products

Organic azides have been exploited since their discovery because of their high reactivities. Various organic reactions using azides have been synthetically applied in chemical biology pharmaceuticals medicinal and agricultural areas. In this review we present some recent applications and developments of organic azides in the total synthesis of natural products (mostly within five years) especially alkaloids. We focus not only on application examples of organic azides but also show their preparation methods including recently reported procedures concerning their decomposing and reducing methods in the syntheses of bioactive molecules.