Mechanistic Manifold and New Developments of the Julia–Kocienski Reaction

Sulfonylation of Pyridyl Phosphonium Salts with Sulfinate Salts in Aqueous Media for the Synthesis of 4-Pyridyl Sulfones via C-P Bond Cleavage

A Na2S2O8-initiated sulfonylation of pyridyl phosphonium salts with sulfinate salts in aqueous media has been developed for facile access to 4-pyridyl sulfones. The reactions, which employed pyridyl phosphonium salts as efficient pyridylation agents via C-P bond activation, showed both broad substrate generality and good functional group compatibility. In addition, the scale-up synthesis and the late-stage modification of pharmaceutically active complex molecules (e.g., loratadine, bisacodyl) could also be successfully realized.

Latest Developments of the Julia-Kocienski Olefination Reaction: Mechanistic Considerations

Since its discovery, the Julia-Kocienski olefination reaction has over past 30 years become one of the key C-C connective methods that is used in late-stage natural product synthesis. The reaction proceeds under mild reaction conditions, with a wide substrate scope and functional group tolerance range and with high (E) selectivity. In this focused review, we discuss the reaction from a mechanistic point of view and disclose key features that play an important role in reaction selectivity. Finally, the mechanistic aspects of the newly developed modification of the Julia-Kocienski reaction, which allows the formation of both (E) and (Z) olefins from the same reaction partners, are discussed.

Total Synthesis of the Allenic Macrolide (+)-Archangiumide

Archangiumide is the first known macrolide natural product comprising an endocyclic allene. For the ring strain that this linear substructure might entail, it was planned to unveil the allene at a very late stage of the projected total synthesis; in actual fact, this was achieved as the last step of the longest linear sequence by using an otherwise globally deprotected substrate. This unconventional timing was made possible by a gold catalyzed rearrangement of a macrocyclic propargyl benzyl ether derivative that uses a -PMB group as latent hydride source to unveil the signature cycloallene; the protecting group therefore gains a strategic role beyond its mere safeguarding function. Although the gold catalyzed reaction per se is stereoablative, the macrocyclic frame of the target was found to impose high selectivity and a stereoconvergent character on the transformation. The required substrate was formed by ring closing alkyne metathesis (RCAM) with the aid of a new air-stable molybdenum alkylidyne catalyst.

19 F-Labeled Probes for Recognition-Enabled Chromatographic 19 F NMR

The NMR technique is among the most powerful analytical methods for molecular structural elucidation, process monitoring, and mechanistic investigations; however, the direct analysis of complex real-world samples is often hampered by crowded NMR spectra that are difficult to interpret. The combination of fluorine chemistry and supramolecular interactions leads to a unique detection method named recognition-enabled chromatographic (REC) 19 F NMR, where interactions between analytes and 19 F-labeled probes are transduced into chromatogram-like 19 F NMR signals of discrete chemical shifts. In this account, we summarize our endeavor to develop novel 19 F-labeled probes tailored for separation-free multicomponent analysis. The strategies to achieve chiral discrimination, sensitivity enhancement, and automated analyte identification will be covered. The account will also provide a detailed discussion of the underlying principles for the design of molecular probes for REC 19 F NMR where appropriate.

Nickel-catalyzed sulfonylative coupling of 2-chlorobenzothiazoles with sulfinates at room temperature

An efficient nickel-catalyzed cross-coupling for the synthesis of 2-sulfonylthiazoles from readily available 2-chlorobenzothiazoles and sodium sulfinates has been developed. A variety of 2-chlorobenzothiazoles and sulfinates having a diverse range of substitution patterns can undergo the coupling process successfully at room temperature. Avoiding the use of precious catalysts and sensitive ligands, moderate to excellent yields of various 2-sulfonylthiazoles were observed.

Nickel-catalyzed desulfonylative olefination of β-hydroxysulfones

A Ni-catalyzed C–O bond activation is used to access alkenes directly from β-hydroxysulfones.

Copper(I)-Catalyzed Cross-Coupling of Arylsulfonyl Radicals with Diazo Compounds: Assembly of Arylsulfones

A novel copper-catalyzed cross-coupling of arylsulfonyl radicals with diazo compounds is described for the synthesis of various arylsulfones under mild conditions. In this reaction, the cheap, environmentally friendly, and readily available inorganic K₂S₂O₅ is employed as the sulfur dioxide source for providing arylsulfonyl radicals. In addition, a radical mechanism involving the insertion of sulfur dioxide with aryl radicals followed by the coupling of arylsulfonyl radicals with copper carbenes is proposed.

Tricomponent Decarboxysulfonylative Cross-Coupling Facilitates Direct Construction of Aryl Sulfones and Reveals a Mechanistic Dualism in the Acridine/Copper Photocatalytic System

Dual catalytic systems involving photocatalytic activation and transition metal-catalyzed steps have enabled innovative approaches to the construction of carbon-carbon and carbon-heteroatom bonds. However, the mechanistic complexity of the dual catalytic processes presents multiple challenges for understanding of the roles of divergent catalytic species that can impede the development of future synthetic methods. Here, we report a dual catalytic process that enables the previously inaccessible, broad-scope, direct conversion of carboxylic acids to aromatic sulfones-centrally important carbonyl group bioisosteric replacements and synthetic intermediates-by a tricomponent decarboxysulfonylative cross-coupling with aryl halides. Detailed mechanistic and computational studies revealed the roles of the copper catalyst, base, and halide anions in channeling the acridine/copper system via a distinct dual catalytic manifold. In contrast to the halide-free decarboxylative conjugate addition that involves cooperative dual catalysis via low-valent copper species, the halide counteranions divert the decarboxysulfonylative cross-coupling with aryl halides through a two-phase, orthogonal relay catalytic manifold, comprising a kinetically coupled (via antithetical inhibitory and activating roles of the base in the two catalytic cycles), mechanistically discrete sequence of a photoinduced, acridine-catalyzed decarboxylative process and a thermal copper-catalyzed arylative coupling. The study underscores the importance of non-innocent roles of counteranions and key redox steps at the interface of catalytic cycles for enabling previously inaccessible dual catalytic transformations.

Functional group divergence and the structural basis of acridine photocatalysis revealed by direct decarboxysulfonylation

The reactivity of the sulfonyl group varies dramatically from nucleophilic sulfinates through chemically robust sulfones to electrophilic sulfonyl halides-a feature that has been used extensively in medicinal chemistry, synthesis, and materials science, especially as bioisosteric replacements and structural analogs of carboxylic acids and other carbonyls. Despite the great synthetic potential of the carboxylic to sulfonyl functional group interconversions, a method that can convert carboxylic acids directly to sulfones, sulfinates and sulfonyl halides has remained out of reach. We report herein the development of a photocatalytic system that for the first time enables direct decarboxylative conversion of carboxylic acids to sulfones and sulfinates, as well as sulfonyl chlorides and fluorides in one step and in a multicomponent fashion. A mechanistic study prompted by the development of the new method revealed the key structural features of the acridine photocatalysts that facilitate the decarboxylative transformations and provided an informative and predictive multivariate linear regression model that quantitatively relates the structural features with the photocatalytic activity.

The influence of α-coordinating groups of aldehydes on E/Z-selectivity and the use of quaternary ammonium counter ions for enhanced E-selectivity in the Julia-Kocienski reaction

Modified reaction conditions for improved E-selectivity of olefins in the Julia-Kocienski reaction of aldehydes having α-coordinating substituents are demonstrated. The chelating groups in aldehydes are expected to stabilize the syn-transition state with metal ions, whereas the weakly coordinating quaternary ammonium ions are devoid of all possible chelating interactions to enhance E-selectivity. A systematic investigation is presented to study the size of the neighbouring protecting groups of aldehydes and their chelation effect on E/Z-selectivity in the Julia-Kocienski reaction.

Recent Advancement on Decarbonylation Reactions Assisted by Ru-complexes: Synthetic and Mechanistic Approach

This frontier article covers the recent advancements in the ruthenium complex catalysed decarbonylation reactions of different types of carbonyl compounds and provides a direction towards the mechanistic understanding involved in...

Cobalt-Catalyzed Hartung-Mukaiyama Cyclization of γ-Hydroxy Olefins: Stereocontrolled Synthesis of the Tetrahydrofuran Moiety of Amphidinolide N

Cobalt-catalyzed Mukaiyama-type cyclization of γ-hydroxy olefins is known as an atom- and step-economical means for stereoselective synthesis of 2,5-trans-substituted tetrahydrofuran derivatives. In this study, we investigated the synthesis of a series of 2,5-substituted tetrahydrofuran derivatives by means of a cobalt-catalyzed Hartung-Mukaiyama cyclization. The stereochemical consequence of the reaction was found to be largely dependent on the substitution pattern and relative configuration of γ-hydroxy olefins. 2,5-cis-Substituted tetrahydrofuran derivatives could be obtained diastereoselectively from appropriately substituted γ-hydroxy olefins. Additionally, relatively bulky olefin substituents and unprotected hydroxy groups at non-interfering positions (e.g., α and δ) were well tolerated in the reaction. Finally, the synthetic versatility of the Hartung-Mukaiyama cyclization was demonstrated through a stereocontrolled synthesis of the tetrahydrofuran moiety of amphidinolide N, a potent cytotoxic macrolide of marine origin. This study expands the capacity of Mukaiyama-type cyclization in that it can be used in convergent assembly of complex tetrahydrofuran motifs from internal olefins.

High Chemo-/Stereoselectivity for Synthesis of Polysubstituted Monofluorinated Pyrimidyl Enol Ether Derivatives

A novel intramolecular Smiles rearrangement of α-fluoro-β-keto-pyrimidylsulfones (usually used as a carbon nucleophile) was developed, providing a versatile avenue for synthesis of tri/tetra-substituted monofluorinated pyrimidyl enol ethers. Among these, diverse (Z)-monofluorovinylsulfones and sulfinates were efficiently assembled by adding extra electrophile and fine-tuning reaction conditions. The process is triggered by a keto-enol tautomerism from enol oxyanion to pyrimidine 2-carbon, completely different from the classical carbon nucleophilic addition reaction approach.

Copper Catalyzed C(sp3)-H Bond Alkylation via Photoinduced Ligand-to-Metal Charge Transfer

Utilizing catalytic CuCl₂ we report the functionalization of numerous feedstock chemicals via the coupling of unactivated C(sp³)-H bonds with electron-deficient olefins. The active cuprate catalyst undergoes Ligand-to-Metal Charge Transfer (LMCT) to enable the generation of a chlorine radical which acts as a powerful hydrogen atom transfer reagent capable of abstracting strong electron-rich C(sp³)-H bonds. Of note is that the chlorocuprate catalyst is an exceedingly mild oxidant (0.5 V vs SCE) and that a proposed protodemetalation mechanism offers a broad scope of electron-deficient olefins, offering high diastereoselectivity in the case of endocyclic alkenes. The coupling of chlorine radical generation with Cu reduction through LMCT enables the generation of a highly active HAT reagent in an operationally simple and atom economical protocol.

Structure determination, correction, and disproof of marine macrolide natural products by chemical synthesis

Integration of chemical synthesis, NMR spectroscopy, and various analytical means is key to success in the structure elucidation of stereochemically complex marine macrolide natural products.

Total synthesis and complete configurational assignment of amphirionin-2

Amphirionin-2 is a linear polyketide metabolite that exhibits potent and selective cytotoxic activity against certain human cancer cell lines. We disclose herein the first total synthesis of amphirionin-2 and determination of its absolute configuration. Our synthesis featured an extensive use of cobalt-catalyzed Mukaiyama-type cyclization of γ-hydroxy olefins for stereoselective formation of all the tetrahydrofuran rings found in the natural product, and a late-stage Stille-type coupling for convergent assembly of the entire carbon backbone. Four candidate diastereomers of amphirionin-2 were synthesized in a unified, convergent manner, and their spectroscopic/chromatographic properties were compared with those of the authentic material. The present study culminated in the reassignment of the C5/C7 relative configuration, assignment of the C12/C18 relative configuration, and determination of the absolute configuration of amphirionin-2.

Inspirations from tetrafibricin and related polyketides: new methods and strategies for 1,5-polyol synthesis

Covering: up to 2019 Selective synthesis with control of remote stereogenic centers has long been a challenge in organic chemistry. In recent years the interest in this topic has been energized by isolation and synthetic studies of tetrafibricin and other natural products containing 1,5-polyols, such as amphidinol 3, marinomycins, and caylobolide. Here we discuss recent developments in 1,5-polyol synthesis, including an overview of selected bioactive natural products in this class and examples of new synthetic methodologies and strategies dedicated to remote stereocontrol in these structures. To illustrate in greater depth, we review several instructive examples of how these innovations have been applied in synthetic studies on tetrafibricin.

Stereodivergent routes in organic synthesis: marine natural products, lactones, other natural products, heterocycles and unnatural compounds

Enantio- and diastereodivergent routes to marine-origin natural products with different sizes of cyclic ethers and lactones have been used in order to assign stereochemical features. Kainoid amino acids such as isodomoic acids have been synthesized using diastereodivergent routes. The bis(indole) alkaloid dragmacidin F has been prepared by enantiodivergent strategies as well as furanoterpenes and the tetracyclic agelastatin A. Natural products containing five-membered lactones like quercus lactones, muricatacins, goniofufuranones, methylenolactocins and frenolicin B have been synthesized using stereodivergent routes. Macrolides are very abundant lactones and have been mainly prepared from the corresponding seco-acids by lactonization, such as lasiodiplodin, zaeralanes, macrosphelides and haloprins, or by ring-closing metathesis, such as aspercyclides, microcarpalides, macrolides FD-891 and 892, and tetradic-5-en-9-olides. Other natural products including cyclic ethers (such as sesamin, asarinin, acetogenins, centrolobines and nabilones), alcohols (such as sulcatol), esters (such as methyl jasmonates), polycyclic precursors of fredericamycin, amino alcohols (such as ambroxol and sphingosines), isoprostanes, isofurans, polyketide precursors of anachelins, brevicomins, gummiferol, shikimic acid and the related compounds, and the pheromone disparlure have been synthesized stereodivergently. Heterocyclic systems such as epoxides, theobroxides and bromoxones, oxetan-3-ones, 5- to 8-membered cyclic ethers, azetidones, γ-lactams, oxazolidinones, bis(oxazolines), dihydropyridoisoindolines and octahydroisoquinolines have been prepared following stereodivergent routes. Stereodivergent routes to unnatural compounds such as alkenes, dienes, allenes, cyclopropanes, alcohols, aldols, amines, amino alcohols, β-amino acids, carboxylic acids, lactones, nitriles and α-amino nitriles have been considered as well.

Stereoselective Synthesis of Trisubstituted (Z)-Alkenes from Ketones via the Julia-Kocienski Olefination Using 1-Methyl- and 1-tert-Butyl-1H-tetrazol-5-yl Alkyl Sulfones

1-Methyl-1H-tetrazol-5-yl (MT) alkyl sulfones 1b, 3b, and 7b react with various unsymmetrical ketones in the presence of LiHMDS in THF at low temperature to give trisubstituted (Z)-alkenes in good yields stereoselectively (Z/E = 91:9 to 99:1). For sterically less demanding ketones, olefination using t-Bu reagents 1d and 3d generated (Z)-alkenes with higher stereoselectivity (93:7-99:1).

Photoredox Generation of Sulfonyl Radicals and Coupling with Electron Deficient Olefins

Various sulfone tetrazoles were activated via iridium photoredox catalysis in the presence of DMAP to give dialkyl sulfones. The presumed sulfone radical intermediates were trapped by a range of electron-deficient olefins in generally good to excellent yields.

Synthetic studies on palmerolide C: synthesis of an advanced intermediate towards the revised structure of palmerolide C

A stereoselective synthesis of the highly advanced intermediates towards the revised structure of palmerolide C and 10-epi-palmerolide C is described in this paper. The required key fragments C1-C6, C7-C14 and C15-C23 have been successfully assembled in a convergent manner to access the C1-C23 framework bearing all the five stereocenters present in the natural product. The synthesis involves the Julia-Kocienski reaction, Yamaguchi esterification, Takai olefination and regioselective epoxide opening as key steps. The proposed route is flexible and could also be applied to the synthesis of structurally related palmerolides.

Methylenation for Aldehydes and Ketones Using 1-Methylbenzimidazol-2-yl Methyl Sulfone

The methylenation reagent 1-methylbenzimidazol-2-yl methyl sulfone 2 reacts with various aldehydes and ketones in the presence of t-BuOK (room temperature, 1 h) in dimethylformamide to give the corresponding terminal alkenes generally in high yields. For sensitive substrates, the reaction is better carried out at low temperature using sodium hexamethyldisilazide in 1,2-dimethoxyethane. The byproduct is easily removed from the products, and the reaction conditions are mild and practical. Reagent 2 can be easily prepared from commercially available 2-mercaptobenzimidazole 5 in 95% yield without any expensive reagents.

Asymmetric total syntheses of naturally occurring α,β-enone-containing RALs, L-783290 and L-783277 through intramolecular base-mediated macrolactonization reaction

Asymmetric total synthesis of two naturally occurring α,β-enone containing RALs, L-783290 and L-783277 is described in this article. An E-selective Horner-Wadsworth-Emmons (HWE) olefination was used as a key reaction to construct the C7'-C8' olefinic unsaturation in L-783290. An enantiopure alkyne addition to the aldehyde followed by Z-selective partial reduction was employed to construct the C7'-C8' olefinic unsaturation in L-783277. Biomimetic lactonization reaction was used to construct the macrolactone core in both the target molecules.

Resveratrol: a review of plant sources, synthesis, stability, modification and food application

Resveratrol, a stilbene molecule belonging to the polyphenol family, is usually extracted from a great many natural plants. The technologies of preparation and extraction methods are developing rapidly. As resveratrol has many beneficial properties, it has been widely utilized in food and medicine industry. In terms of its structure, it is susceptible to degradation and can undergo chemical changes during food processing. Different studies have therefore given more attention to various aspects of resveratrol, including anti-aging, anti-oxidant, and anti-cancer activity. This review classifies the study of resveratrol, considers plant sources, synthesis, stability, common reactions, and food applications, and provides references to boost its food and medical utilization. © 2019 Society of Chemical Industry.

Emergence of 2,3,5-trisubstituted tetrahydrofuran natural products and their synthesis

The emergence of various 2,3,5-trisubstituted tetrahydrofuran natural products in the recent literature and their synthesis is the focus of this review. These molecules exhibit varied bioactivities and have garnered the interest of several synthetic chemists owing to their efficient synthesis. A few of them have been synthesized and their absolute stereo structure has been confirmed for the first time. These will be appealing candidates in future synthetic investigations along with the untouched molecules. Thus, this compilation will reveal these molecules for expansion of their diversity within the realm of both synthesis and bioactivity studies.

First synthesis and absolute configuration of phorbasin H, a diterpene carboxylic acid isolated from the sponge Phorbas gukulensis

The first synthesis of phorbasin H, a diterpene carboxylic acid isolated from the sponge Phorbas gukulensis, was achieved using 1,4-trans-cyclohexanedimethanol and (S)-citronellal as starting materials. The data collected in this synthesis indicated the absolute configuration of the naturally occurring phorbasin H to be S.

Total Synthesis and Antimicrobial Evaluation of 23-Demethyleushearilide and Extensive Antimicrobial Evaluation of All Synthetic Stereoisomers of (16Z,20E)-Eushearilide and (16E,20E)-Eushearilide

A novel stereoisomer of eushearilide, 23-demethyleushearilide, was synthesized, and the structure–activity relationships of this compound along with known eushearilide stereoisomers were investigated in order to design novel lead compounds for the treatment of fungal infections. It was discovered that all of these congeners, together with the natural product, exhibited a wide range of antimicrobial activity against not only fungi but also against bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE).

Stereochemical Revision, Total Synthesis, and Solution State Conformation of the Complex Chlorosulfolipid Mytilipin B

Chlorosulfolipids constitute a structurally intriguing and synthetically challenging class of marine natural products that are isolated from mussels and freshwater algae. The most complex structure from this family of compounds is currently represented by Mytilipin B, isolated in 2002 from culinary mussel Mytilus galloprovincialis, whose initially proposed structure was shown to be incorrect. In this study, we present the synthesis of four diastereomers which allowed the reassignment of eight stereocenters and the stereochemical revision of Mytilipin B, along with the determination of the dominant solution-state conformation.

Structure Determination of a Chloroenyne from Laurencia majuscula Using Computational Methods and Total Synthesis

Despite numerous advances in spectroscopic methods through the latter part of the 20th century, the unequivocal structure determination of natural products can remain challenging, and inevitably, incorrect structures appear in the literature. Computational methods that allow the accurate prediction of NMR chemical shifts have emerged as a powerful addition to the toolbox of methods available for the structure determination of small organic molecules. Herein, we report the structure determination of a small, stereochemically rich natural product from Laurencia majuscula using the powerful combination of computational methods and total synthesis, along with the structure confirmation of notoryne, using the same approach. Additionally, we synthesized three further diastereomers of the L. majuscula enyne and have demonstrated that computations are able to distinguish each of the four synthetic diastereomers from the 32 possible diastereomers of the natural product. Key to the success of this work is to analyze the computational data to provide the greatest distinction between each diastereomer, by identifying chemical shifts that are most sensitive to changes in relative stereochemistry. The success of the computational methods in the structure determination of stereochemically rich, flexible organic molecules will allow all involved in structure determination to use these methods with confidence.

Asymmetric total synthesis of cryptoconcatone I

Asymmetric total synthesis of the naturally occurring cryptoconcatone I, which possesses a γ-Z-butenolide framework, is described here for the first time. Asymmetric propargylation, E-selective cross metathesis, and regioselective reductive epoxide ring opening were employed to access the enantiopure terminal alkyne. Late stage bimetallic cascade cyclization of the alkyne with (Z)-3-bromoacrylic acid afforded the natural product in an efficient way.

Stereodivergent synthesis of alkenes by controllable syn-/anti-fragmentation of β-hydroxysulfonyl intermediates

Complementary fragmentation mechanisms of Hawkins and one-pot Julia olefinations were employed for the stereodivergent synthesis of alkenes.