Olefination Reactions of Phosphorus-Stabilized Carbon Nucleophiles

Application of the Horner-Wadsworth-Emmons Olefination in the Construction of E-α,β-Unsaturated β-Boryl Nitriles

Herein, we describe a simple transition-metal-free synthesis of E-α,β-unsaturated β-boryl nitriles by the Horner-Wadsworth-Emmons reaction starting from potassium acyltrifluoroborates. The methodology encompasses a broad range of alkyl and aryl substrates. The reaction conditions are simple, and the reaction products are in most cases isolated with good yields as pure E isomers without column chromatography.

Chemical modification for improving drug-like molecular properties of climacostol, a natural resorcinolic lipid

Small organic molecules are compounds that are manufactured through chemical synthesis. One of the key advantages of small molecules is that they have a low molecular weight and simple chemical structures. This allows more predictability to their pharmacokinetics and pharmacodynamics, which means that dosing is simpler. To use small molecules as a useful tool to address human health issues, the collaboration between disciplines, especially chemistry and biology, is essential. In recent years in our laboratories, we have demonstrated that climacostol, a 5-alkenyl resorcinolic produced by eukaryotic microorganisms as secondary metabolite and obtained by our synthetic strategy too, it shows important biological and pharmacological activities. These ones are highly dependent on the 5-alkenyl chain, and chemical modifications to the resorcinolic moiety can be exploited to achieve higher toxicity against pathogen microbes and protists than climacostol. In this study, we have designed and made a synthetic strategy for a new analogue of climacostol (AN3), and evaluated how the new hydroxyl group at position four in the aromatic ring influences its biological effects on prokaryotic and free-living protists and on non-target cells/organisms, especially with regard to cytotoxic properties.

Non-Ionic Peterson-Type Olefination Reactivity and its Use in a Silicon-Promoted Carbonyl-Carbonyl Cross Coupling Reaction

The [2+2] cycloaddition reaction between the Si=C double bond of adamantylsilene and the carbonyl group of aliphatic, aromatic or acetylenic ketones and aldehydes is demonstrated. The product of this reaction that is central to a non-ionic version of the Peterson olefination is an unusual four-membered 1,2-silaoxetane heterocycle that was characterized spectroscopically and crystallographically. In the presence of SiO2, the silaoxetane undergoes retro-cycloaddition with the formation of alkene products. As the [2+2] cycloaddition proceeds without the necessity of any base, enolizable ketones can be converted into olefins. In addition, it is shown that the adamantylsilene can be produced in situ by a sila-Peterson reaction, providing valuable input for the development of a new one-pot silicon-based reductive carbonyl-carbonyl cross coupling methodology.

Mechanism of Z-Selective Allylic Functionalization via Thianthrenium Salts

A detailed mechanistic study of the Z-selective allylic functionalization via thianthrenium salts is presented. Kinetic analyses, deuterium labeling experiments, and computational methods are used to rationalize the observed reactivity and selectivity. We find that the reaction proceeds via a rate-determining and stereodetermining allylic deprotonation of an alkenylthianthrenium species. The Z-configuration of the resultant allylic ylide is translated into the Z-allylic amine product through a sequence of subsequent fast and irreversible steps: protonation to form a Z-allylic thianthrenium electrophile and then regioselective substitution by the nucleophile. In the stereodetermining deprotonation step, computational studies identified a series of stabilizing nonbonding interactions in the Z-alkene-forming transition state that contribute to the stereoselectivity.

Regio- and Stereoselective Intermolecular Oxysulfonylation of Alkynes with 1,3-Diketones to Access (Z)-β-Sulfonated Enethers

The first multicomponent regio- and stereoselective difunctionalization of alkynes via concomitant C-O and C-S bond formation using 1,3-diketones and sodium sulfinate has been developed for the synthesis of various sulfonated enethers. The viability of this strategy is unveiled by gram-scale, various synthetic modifications and late-stage functionalization. This transformation does not require any prefunctionalization, metal catalysts, and oxidants. The present operationally simple, efficient, and sustainable approach provides various functionalized olefins in a one-pot protocol with high Z-selectivity.

Advances in the application of named reactions in polymer synthesis

With the development of polymer science, more and more named reactions have been applied to synthesizing polymers. Introducing new reactions into polymer synthesis is undoubtedly an excellent expansion for monomer and polymer libraries. In this review, the named reactions employed in polymer-chain synthesis were divided into seven types: electrophilic reactions, nucleophilic reactions, transition metal-mediated cross-coupling reactions, free radical reactions, pericyclic reactions, multi-component reactions and rearrangement reactions. The discussion was mainly focused on the progress in the utilization of these named reactions in polymer synthesis, which could be a valuable reference for researchers in the polymer field.

Stereoselective Synthesis of Bisfuranoxide (Aurochrome, Auroxanthin) and Monofuranoxide (Equinenone 5',8'-Epoxide) Carotenoids by Double Horner-Wadsworth-Emmons Reaction

The stereoselective synthesis of C40-all-trans-carotenoids with the formal hexahydrobenzofuran skeletons aurochrome, auroxanthin, and equinenone-5',8'-epoxide is reported. The synthesis is based on a one-pot or stepwise double Horner-Wadsworth-Emmons (HWE) reaction of a terminal enantiopure C15-5,6-epoxycyclohexadienylphosphonate and a central C10-trienedial. The ring expansion of the epoxycyclohexadienylphosphonate, generated by a Stille cross-coupling reaction, to the hexahydrobenzofuran skeleton was promoted by the reaction conditions of the HWE reaction prior to double-bond formation.

[2 + 2] Cycloaddition of phosphaalkenes as a key step for the reductive coupling of diaryl ketones to tetraaryl olefins

Procedures for the reductive coupling of carbonyl compounds to alkenes in the literature rely either on a radical coupling strategy, as in the McMurry coupling, or ionic pathways, sometimes catalysed by transition metals, as in more contemporary contributions. Herein, we present the first example of a third strategy that is based on the [2 + 2] cycloaddition of ketone-derived phosphaalkenes. Removal of P-trimethylsilyl groups at the intermediary 1,2-diphosphetane dimer results in its collapse and concomitant release of the tetraaryl-substituted alkene. In fact, the presented strategy is the only alternative to the McMurry coupling in the literature that allows tetraaryl alkene formation from diaryl ketones, with yields as high as 85%. The power of the methodology is illustrated in the reaction of tethered bis-benzophenones which engage in intramolecular reductive carbonyl couplings to form unusual macrocycles without the need for high dilution conditions or templating.

Unusual Application for Phosphonium Salts and Phosphoranes: Synthesis of Chalcogenides

A novel strategy for the synthesis of sulfides and selenides from phosphonium salts and thio- or selenesulfonates, commercially available compounds, is described. When phosphoranes were used in the reaction, different products were obtained. The methodology does not require the use of metals, reactive species, or anhydrous conditions to be performed.

Stereoselective synthesis of fully substituted ethylenes via an Ag-catalyzed 1,6-nucleophilic addition/annulation cascade

A catalytic 1,6-nucleophilic addition/annulation cascade was developed for the first time, and used to produce 27 hitherto unreported ethylene-linked 1-naphthol-imidazole pairs with generally good yields and complete stereoselectivity. An Ag₂O-catalyzed reaction of yne-allenone esters with tosylmethyl isocyanide proceeded efficiently, and provided a simple and convergent protocol for the synthesis of fully substituted (Z)-ethylenes whereas tetrasubstituted (E)-ethylenes were obtained when ethyl isocyanoacetate was employed in this transformation. The reaction pathway consists of [2+2] cycloaddition, 1,6-nucleophilic addition and [3+2] cycloaddition, leading to continuous multiple bond-forming events including C-C and C-N bonds to construct complex molecules.

Stereoselective aminosulfonylation of alkynes: an approach to access (Z)-β-amino vinylsulfones

The stereoselective aminosulfonylation of alkynes in a syn mode is accomplished using sodium sulfinates and azoles, in the presence of I₂/base and afforded the (Z)-β-amino vinylsulfones in good yields.

Tandem Catalysis: Transforming Alcohols to Alkenes by Oxidative Dehydroxymethylation

We report a Rh-catalyst for accessing olefins from primary alcohols by a C-C bond cleavage that results in dehomologation. This functional group interconversion proceeds by an oxidation-dehydroformylation enabled by N, N-dimethylacrylamide as a sacrificial acceptor of hydrogen gas. Alcohols with diverse functionality and structure undergo oxidative dehydroxymethylation to access the corresponding olefins. Our catalyst protocol enables a two-step semisynthesis of (+)-yohimbenone and dehomologation of feedstock olefins.

Chemoselective Synthesis of Z-Olefins through Rh-Catalyzed Formate-Mediated 1,6-Reduction

Z-olefins are important functional units in synthetic chemistry; their preparation has thus received considerable attention. Many prevailing methods for cis-olefination are complicated by the presence of multiple unsaturated units or electrophilic functional groups. In this study, Z-olefins are delivered through selective reduction of activated dienes using formic acid. The reaction proceeds with high regio- and stereoselectivity (typically >90:10 and >95:5, respectively) and preserves other alkenyl, alkynyl, protic, and electrophilic groups.

12,13-Aziridinyl Epothilones. Stereoselective Synthesis of Trisubstituted Olefinic Bonds from Methyl Ketones and Heteroaromatic Phosphonates and Design, Synthesis, and Biological Evaluation of Potent Antitumor Agents

The synthesis and biological evaluation of a series of 12,13-aziridinyl epothilone B analogues is described. These compounds were accessed by a practical, general process that involved a 12,13-olefinic methyl ketone as a starting material obtained by ozonolytic cleavage of epothilone B followed by tungsten-induced deoxygenation of the epoxide moiety. The attachment of the aziridine structural motif was achieved by application of the Ess-Kürti-Falck aziridination, while the heterocyclic side chains were introduced via stereoselective phosphonate-based olefinations. In order to ensure high (E) selectivities for the latter reaction for electron-rich heterocycles, it became necessary to develop and apply an unprecedented modification of the venerable Horner-Wadsworth-Emmons reaction, employing 2-fluoroethoxyphosphonates that may prove to be of general value in organic synthesis. These studies resulted in the discovery of some of the most potent epothilones reported to date. Equipped with functional groups to accommodate modern drug delivery technologies, some of these compounds exhibited picomolar potencies that qualify them as payloads for antibody drug conjugates (ADCs), while a number of them revealed impressive activities against drug resistant human cancer cells, making them desirable for potential medical applications.

Cinnamaldehyde Derivatives Inhibit Coxsackievirus B3-Induced Viral Myocarditis

The chemical property of cinnamaldehyde is unstable in vivo, although early experiments have shown its obvious therapeutic effects on viral myocarditis (VMC). To overcome this problem, we used cinnamaldehyde as a leading compound to synthesize derivatives. Five derivatives of cinnamaldehyde were synthesized: 4-methylcinnamaldehyde (1), 4-chlorocinnamaldehyde (2), 4-methoxycinnamaldehyde (3), α-bromo-4-methylcinnamaldehyde (4), and α-bromo-4-chlorocinnamaldehyde (5). Neonatal rat cardiomyocytes and HeLa cells infected by coxsackievirus B3 (CVB3) were used to evaluate their antiviral and cytotoxic effects. In vivo BALB/c mice were infected with CVB3 for establishing VMC models. Among the derivatives, compound 4 and 5 inhibited the CVB3 in HeLa cells with the half-maximal inhibitory concentrations values of 11.38 ± 2.22 μM and 2.12 ± 0.37 μM, respectively. The 50% toxic concentrations of compound 4 and 5-treated cells were 39-fold and 87-fold higher than in the cinnamaldehyde group. Compound 4 and 5 effectively reduced the viral titers and cardiac pathological changes in a dose-dependent manner. In addition, compound 4 and 5 significantly inhibited the secretion, mRNA and protein expressions of inflammatory cytokines TNF-α, IL-1β and IL-6 in CVB3-infected cardiomyocytes, indicating that brominated cinnamaldehyde not only improved the anti-vital activities for VMC, but also had potent anti-inflammatory effects in cardiomyocytes induced by CVB3.

Applicable β-sulfonium carbanions: facile construction of thiophene derivatives

A sequence of Sonogashira coupling, propargyl-allenyl isomerization, intramolecular addition and [3, 3] sigmatropic rearrangement affords thiophene derivatives.

Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(-)-myrtenol nitrate

Here we report the chemoselective synthesis of several important, climate relevant isoprene nitrates using silver nitrate to mediate a 'halide for nitrate' substitution. Employing readily available starting materials, reagents and Horner-Wadsworth-Emmons chemistry the synthesis of easily separable, synthetically versatile 'key building blocks' (E)- and (Z)-3-methyl-4-chlorobut-2-en-1-ol as well as (E)- and (Z)-1-((2-methyl-4-bromobut-2-enyloxy)methyl)-4-methoxybenzene has been achieved using cheap, 'off the shelf' materials. Exploiting their reactivity we have studied their ability to undergo an 'allylic halide for allylic nitrate' substitution reaction which we demonstrate generates (E)- and (Z)-3-methyl-4-hydroxybut-2-enyl nitrate, and (E)- and (Z)-2-methyl-4-hydroxybut-2-enyl nitrates ('isoprene nitrates') in 66-80% overall yields. Using NOESY experiments the elucidation of the carbon-carbon double bond configuration within the purified isoprene nitrates has been established. Further exemplifying our 'halide for nitrate' substitution chemistry we outline the straightforward transformation of (1R,2S)-(-)-myrtenol bromide into the previously unknown monoterpene nitrate (1R,2S)-(-)-myrtenol nitrate.

Construction of highly functionalized naphthalenes using an in situ ene–allene strategy

Construction of highly functionalized naphthalene derivatives remains a challenging task for organic chemists because of the effect of the substituent.

Z-Selective Olefin Synthesis via Iron-Catalyzed Reductive Coupling of Alkyl Halides with Terminal Arylalkynes

Selective catalytic synthesis of Z-olefins has been challenging. Here we describe a method to produce 1,2-disubstituted olefins in high Z selectivity via reductive cross-coupling of alkyl halides with terminal arylalkynes. The method employs inexpensive and nontoxic catalyst (iron(II) bromide) and reductant (zinc). The substrate scope encompasses primary, secondary, and tertiary alkyl halides, and the reaction tolerates a large number of functional groups. The utility of the method is demonstrated in the synthesis of several pharmaceutically relevant molecules. Mechanistic study suggests that the reaction proceeds through an iron-catalyzed anti-selective carbozincation pathway.

Poly(phosphonate)-mediated Horner–Wadsworth–Emmons reactions

Poly(phosphonate)s were used in Horner–Wadsworth–Emmons (HWE) reactions with aldehydes. The progress of the reaction was monitored via in situ-NMR spectroscopy. Minimal purification efforts by precipitation of the polymer are achieved.

Synthesis of labile all-trans-7,8,7′,8′-bis-acetylenic carotenoids by bi-directional Horner–Wadsworth–Emmons condensation

Two symmetrical C₇,C₈-acetylenic carotenoids have been stereoselectively prepared using a bi-directional Horner–Wadsworth–Emmons condensation of the C₁₀-dialdehyde and C₁₅-phosphonates.

Palladium-catalyzed intermolecular Heck reaction of alkyl halides

An efficient Pd-catalyzed method for intermolecular Heck reaction of common alkyl halides is described for the first time.