Horner-Wadsworth-Emmons Research Articles

Stereocontrolled Synthesis of Harzialactone A and Its Three Stereoisomers by Use of Standardized Polyketide Building Blocks

In this paper, we present a short and convenient synthesis of the natural product Harzialactone A and its three stereoisomers. In a three‐step synthesis starting from cheap and commercially available benzaldehyde, we created the small polyketidic compound with full control over its two stereogenic centers. To this end, we employed a chiral building block previously described by us, introducing the first stereogenic center through a Horner–Wittig reaction. The second stereogenic center was installed via stereocontrolled syn‐ or anti‐reduction with the corresponding β‐hydroxy ketone intermediates. Upon ozonolysis followed by oxidation the natural product and its stereovariants were produced with excellent enantio‐ and diastereopurities.

Synthesis and polymerization of 2,2'-bithiophenes substituted with π-conjugated arms

A variety of 2,2′-bithiophene derivatives with different π-conjugated arms at the 3,3′-positions have been synthesized and evaluated as suitable building blocks for the preparation of functional conjugated polymers. Polymerizations have been carried out through either Horner-Wadsworth-Emmons (HWE) or Stille cross coupling reactions with appropriate comonomers. Whereas the polymerization of 5,5′-diformyl- and 5,5′-dibromo-2,2′-bithiophenes did not extend beyond a small number of monomer units, 5,5′-bis(4-formylphenyl)-2,2′-bithiophenes formed polymers with high molecular weights, narrow polydispersity and good thermal stability. A preliminary study of the UV and photoluminescence properties of the prepared compounds is also presented.

Design, synthesis and biological evaluation of novel 2-alkylidene 19-norcalcitriol analogs

Continuing our studies aimed at A-ring modified vitamin D compounds, we designed novel 19-norcalcitriol derivatives bearing at C-2 pegylated chains of different lengths. The terminal fragments of these substituents contain hydroxyls or moieties possessing nitrogen and/or sulfur atoms capable of transition metal ions complexation. Also, two conjugate–type platinum(II) complexes of 19-norcalcitriol were obtained in which l-methionine served as chelating moiety. The convergent synthesis of the target 19-norcalcitriol analogs involved several steps with the crucial one being condensation of A-ring phosphine oxide and the known Grundmann ketone by Wittig-Horner reaction. Further elaboration of the 2-alkylidene substituent provided all final compounds which were then tested to determine their affinity for the vitamin D receptor and cytotoxic activity.

Still–Gennari Olefination and its Applications in Organic Synthesis

AbstractThe Still–Gennari olefination is a widely applied modification of the Horner–Wadsworth–Emmons reaction, allowing access to Z‐olefins by carbonyl group transformation. Its synthetic utility is undoubtedly of great significance for organic chemistry, as can be illustrated by the number of citations of the original report by W. C. Still and C. Gennari which up to date has been cited over 1000 times. In 2008 Nobel prize winner Ei‐ichi Negishi indicated the Still–Gennari olefination as one of the crucial methods for tolefin synthesis, complementary to palladium‐catalyzed alkenylations. Surprisingly, so far there is no review concerning this popular and valuable transformation. Therefore, we aim to comprehensively systematize achievements in this field and to present the scope of applications of the Still–Gennari olefination along with recent examples in the total synthesis of biologically active compounds. Our review is intended to be of interest for the general chemical community as well as to be a helpful source of information for synthetic organic chemists.magnified image

Syntheses and Reactions of Pyrroline, Piperidine Nitroxide Phosphonates.

Organophosphorus compounds occupy a significant position among the plethora of organic compounds, but a limited number of paramagnetic phosphorus compounds have been reported, including paramagnetic phosphonates. This paper describes the syntheses and further transformations of pyrroline and piperidine nitroxide phosphonates by well-established methods, such as the Pudovik, Arbuzov and Horner-Wadsworth-Emmons (HWE) reactions. The reaction of paramagnetic α-bromoketone produced a vinylphosphonate in the Perkow reaction. Paramagnetic α-hydroxyphosphonates could be subjected to oxidation, elimination and substitution reactions to produce various paramagnetic phosphonates. The synthesized paramagnetic phosphonates proved to be useful synthetic building blocks for carbon-carbon bond-forming reactions in the Horner-Wadsworth-Emmons olefination reactions. The unsaturated compounds achieved could be transformed into various substituted pyrroline nitroxides, proxyl nitroxides and paramagnetic polyaromatics. The Trolox® equivalent antioxidant capacity (TEAC) of new phosphonates was also screened, and tertiary α-hydroxyphosphonatate nitroxides exhibited remarkable antioxidant activity.

Synthesis of Gemini analogs of 19-norcalcitriol and their platinum(II) complexes

Hormonally active vitamin D3 metabolite, calcitriol, plays an important role in calcium-phosphate homeostasis, immune system actions and cell differentiation. Although anticancer activity of calcitriol is well documented and thousands of its analogs have been synthesized, none has been approved as a potential drug against cancer. Therefore, we attempted to introduce the cytotoxic effect to the calcitriol molecule by its linking to cisplatin. Herein, we present the synthesis of vitamin D compounds, designed on the basis of molecular modeling and docking experiments to the vitamin D receptor, and characterized by the presence of significantly different two side chains attached to C-20. In this study, a new synthetic approach to Gemini analogs was developed. Preparation of the target 19-norcalcitriol compounds involved separate syntheses of several building blocks (the A-ring, C/D-rings and side-chain fragments). The convergent synthetic strategy was used to combine these components by the different coupling processes, the crucial one being Wittig-Horner reaction of the Grundmann ketone analog with the known 2-methylene A-ring phosphine oxide. Due to the nature of the constructed steroidal side chains (bidentate ligands), which allowed coordination of metal ions, the first conjugate-type platinum(II) complexes of the vitamin D analogs were also successfully prepared and characterized. The target vitamin D compounds, displaying significant affinity for a vitamin D receptor, were assessed in vitro for their anti-proliferative activities towards several cell lines.

Stereoselective Synthesis of the C1-C16 Fragment of the Purported Structure of Formosalide B.

The first stereoselective synthesis of the C1–C16 fragment possessing stereo-enriched fully substituted tetrahydropyran (THP) along with tetrahydrofuran (THF) rings of the proposed structure of formosalide B is described in 12 longest linear steps with 22% overall yield, starting from two cheap and commercially available 1,5-pentanediol and l-glutamic acid, following a convergent approach. The key steps involve in this synthesis are Horner–Wadsworth–Emmons reaction, Sharpless asymmetric dihydroxylation, and acid-mediated ketalization to assemble the substituted THP ring, one-pot Sharpless dihydroxylation–SN2-type cyclization, and Wittig homologation to construct the THF derivative.

Synthetic Approaches to Contemporary Drugs that Contain the Cyclopropyl Moiety

The U.S. Food and Drug Administration approved 18 new drugs that incorporate the cyclopropyl structural motif in the time frame from 2012 to 2018. This review provides an overview of synthetic approaches to these drugs with emphasis on the construction of the cyclopropyl moiety or its incorporation into the key building blocks for assembly of the highlighted drugs. Based on the structural diversity of these drugs, synthetic approaches for the construction and introduction of the cyclopropyl moiety into their structure are diverse and include: cycloalkylation (double alkylation) of CH-acids, catalytic cyclopropanation of alkenes with diazo compounds, the Simmons–Smith reaction, the Corey–Chaykovsky reaction, the Kulinkovich reaction, the Horner–Wadsworth–Emmons reaction, and cycloaddition. In addition, the cyclopropyl structure was also introduced into the drug substance intermediates via simple cyclopropyl-moiety-containing building blocks, such as cyclopropylamine, cyclopropanesulfonamide, cyclopropanecarbonyl chloride, and cyclopropylmagnesium bromide.1 Introduction2 Synthesis of Recently Approved Cyclopropyl-Moiety-Containing Drugs2.1 Cabozantinib2.2 Trametinib2.3 Simeprevir2.4 Ledipasvir2.5 Olaparib2.6 Tasimelteon2.7 Finafloxacin2.8 Paritaprevir2.9 Lenvatinib2.10 Lumacaftor2.11 Lesinurad2.12 Grazoprevir2.13 Glecaprevir2.14 Ozenoxacin2.15 Voxilaprevir2.16 Naldemedine2.17 Tezacaftor2.18 Tecovirimat3 Conclusion

The proposed structures of phenolic compounds isolated from Piper betle L. differ from those of the compounds obtained by total synthesis

We describe the syntheses of phenolic compounds, 4-[(1E, 3E, 5E)−6-(4-octyloxyphenyl)hexa-1,3,5-trien-1-yl]benzene-1,2-diol (1) and 3-(n-dodecyloxy) phenol (2), isolated from Piper betle. The triene moiety of 4-[(1E, 3E, 5E)−6-(4-octyloxyphenyl)hexa-1,3,5-trien-1-yl]benzene-1,2-diol was formed via two different methods, the Horner–Wadsworth–Emmons reaction and the McMurry coupling reaction. The spectral data of synthesized compounds show differences with those of reported as the naturally occurring compounds.

Efficient Synthesis of Long‐wavelength Absorbing Cyanochlorophyll a Derivatives via Stereoselective Horner–Wadsworth–Emmons Reaction

In this article, we report the stereoselective Horner–Wadsworth–Emmons reaction of reactive carbonyl‐substituted chlorophyll a derivatives with diethyl cyanomethylphosphonate. We found that the formyl or keto group at the chlorin periphery can react stereoselectively with phosphonate carbanions to produce a series of cyanomethylene‐substituted chlorins with predominantly E geometry. Considering that no consistent records are available in the literature on the results of the allomerization of methyl pyropheophorbide a, we propose a reliable process for the transformation of this chlorophyll derivative. Our methodology represents a simple and efficient way for the preparation of novel, differently functionalized long‐wavelength absorbing chlorins, those can be applied for photodynamic therapy, solar cells, and other relevant purposes.

Efficient synthesis of 3-TBDMS-11α,25-dihydroxyvitamin D3 and D2 ethers

Vitamin D deficiency might cause a wide variety of human disorders. As a prerequisite for appropriate diagnosis and therapy, medicinally relevant vitamin D metabolites have to be assayed most accurately and with high specificity. It has been demonstrated, that vitamin D conjugates, linked via a hydroxyl group at C11, might be promising for the development of highly specific antibodies to be employed in competitive protein binding assays. The connective synthesis of 3-TBDMS-11α,25-dihydroxyvitamin D3 and D2 ethers in 500 mg scale, starting from vitamin D2, is described. For installation of a hydroxyl group at C11 a sequence of Pd(OAc)2 mediated oxidation of an enone, epoxidation and subsequent epoxide ring opening was applied to obtain a suitable CD-ring precursor, that was connected with an A-ring diphenylphosphine oxide by Wittig-Horner reaction. Finally, an appropriate side chain was installed, respectively.

The reaction of anthracenyl-α-hydroxyphosphonate with anthracene: Access to diverse (bis)-anthracenylmethylphosphonates as a suitable source for extensive π-conjugates

Molecular anthracene has been used as an arene in the Friedel-Crafts (FC) type arylation reaction of anthracenyl-α-hydroxyphosphonate in the presence of acid. A diverse product formation is observed, in which anthracene unit is found to be linked through its C1 position with α-C of phosphonate. Interestingly, the molecular conformation (X-ray structure) of this phosphonate reveals one of the bond angles of a tetrahedral carbon as 118° which is close to the C of sp2 character. Further, molecular anthracene is also recognized to attack at the C10 position of 9-anthracenylphosphonate through C1 or C2 or C9 atoms and the structures of three isomeric phosphonates are established with the help of 1H and 31P NMR studies. The bis-anthracenyl compounds with a P-CH2 unit have been successfully utilized in Horner-Wadsworth-Emmons (HWE) reactions to afford extensive bis-anthracenyl-linked π-conjugates.

Total Synthesis and Stereochemical Assignment of Penicitide A.

Stereoselective total synthesis of marine secondary metabolite penicitide A has been accomplished for the first time following a convergent approach. The salient feature of this study includes Horner-Wadsworth-Emmons (HWE) olefination, Evans methylations, Crimmins acetate aldol reaction, and cross olefin metathesis. Our synthetic study established the stereochemistry of unassigned C-10 and C-12 centers and also disclosed the absolute configurations of C-3 and C-5 stereocenters.

Synthetic Approaches to Unsymmetrically Substituted 5,7-Dihydroxycoumarins

The chemical equivalence of the hydroxy groups in the 5,7-dihydroxycoumarin core has challenged synthetic chemists to develop short and efficient strategies for the selective modification of one of the hydroxy groups leaving the second intact. Over the past 100 years, chemists have proposed various approaches to distinguishing between these two groups according to their reactivity. While the early syntheses included simple nonselective reactions of both hydroxy groups and the subsequent separation of mixtures of the 5-O- and 7-O-isomers formed, recent sophisticated approaches often include the introduction of protective groups for selective directing reactions or the completely controlled construction of the 5,7-dihydroxycoumarin framework by Horner–Wadsworth–Emmons reaction. This review discusses in detail approaches towards unsymmetrically substituted 5,7-dihydroxycoumarins as well as factors influencing 5-O vs. 7-O regioselectivity of reactions of 5,7-dihydroxycoumarins. This review covers all the literature since 1921 with an emphasis on recent works. This critical review may facilitate the synthesis of new drug candidates as well as the total synthesis of natural products.1 Introduction2 O-Modification of 5,7-Dihydroxycoumarins2.1 Alkylation/Alkenylation2.2 Acylation2.3 Sulfonylation2.4 Silylation2.5 Acylation Followed by Alkylation3 Other Approaches3.1 Synthesis from Substituted Phloroglucinol3.2 Synthesis from Derivatives of 2-Acylphloroglucinol4 Conclusion

An approach to new chiral bicyclic imines and amines via Horner-Wadsworth-Emmons reaction.

New chiral bicyclic imines, enamines and amines were prepared via Horner–Wadsworth–Emmons reaction of hexahydroquinoxalin-2(1H)-one-derived phosphonate, as the source of a phosphonate carbanion, and a wide range of structurally diverse carbonyl substrates. The simplicity of the synthetic protocol, high selectivity, and broad substrate scope are the main advantages of the presented methodology.

Which isomer is it, 1,2,5,6- or 1,4,5,8-tetrasubstituted cycloocta-1,3,5,7-tetraene? Synthesis of symmetrically tetrasubstituted cycloocta-1,3,5,7-tetraene derivatives.

Ni(0) catalyzed cyclotetramerization [(2 + 2 + 2 + 2) cycloaddition] of propargyl alcohol gave D2 symmetric 1,4,5,8-tetrakis(hydroxymethyl)cycloocta-1,3,5,7-tetraene (1) as the major product contrary to what was reported earlier to be the corresponding C2v symmetric isomer, namely 1,2,5,6-tetrakis(hydroxymethyl)cycloocta-1,3,5,7-tetraene. The structure of 1 has been unambiguously assigned on the basis of single crystal XRD data which showed a very interesting "densely" intermolecularly hydrogen bonded solid state supramolecular structure. Tetrabromide (3) prepared from tetra-alcohol (1) reacted with a variety of nucleophiles, namely carbon, nitrogen, sulfur and phosphorus nucleophiles, to give the corresponding derivatives in good yields. The tetraphosphonate derivative (9) underwent the Wittig-Horner reaction with aromatic aldehydes to give the corresponding tetra-styryl derivatives (10a-i). The reaction of tetrabromide with aniline, benzyl amine and R(+)-α-methylbenzyl amine gave the corresponding C2v symmetric pyrroline fused 1,2,5,6-tetra-substituted cycloocta-1,3,5,7-tetraene derivatives, while all the other derivatives belonged to D2 symmetric 1,4,5,8-tetra-substituted cycloocta-1,3,5,7-tetraene. Quantum mechanical calculations support the above conclusion based on the relative stabilities of the two isomers. The fusion of a 5-membered pyrroline ring with the tub-shaped cyclooctatetraene (COT) ring leads to flattening of the tub (shallow tub) making it easier for the ring inversion of COT through a planar intermediate to take place readily resulting in the formation of C2v symmetric pyrroline fused COT derivatives.

Synthesis, molecular docking and biological evaluation of 2-(thiophen-2-yl)-1H-indoles as potent HIV-1 non-nucleoside reverse transcriptase inhibitors.

New 2-(thiophen-2-yl)-1H-indole derivatives bearing hydrophobic substituents at the 3-position were designed, synthesized and evaluated for their inhibition of HIV-1 reverse transcriptase (RT) enzyme. Dialkylphosphites (2a-c) or trialkylphosphites (3a-c) were reacted with 2-(thiophen-2-yl)-1H-indole-3-carbaldehyde (1) yielding the corresponding α-hydroxyphosphonate adducts (7a-7c). The reaction of compound 1 with the ylidenetriphenylphosphoranes (4a-4c) proceeds via Wittig mechanism giving the corresponding ethylenes (E, 8a-c). Compounds 8b,c were equally obtained upon reacting aldehyde 1 with the appropriate dialkylphosphonates 5a,b under the Horner-Wittig reaction conditions. On the other hand, the reaction of aldehyde 1 with diethyl cyanomethylene phosphonate (5c) yielded a mixture of the E-ethylene 10 and the cyanovinyl phosphonate 11. The thioaldehyde 12 was obtained upon refluxing aldehyde 1 with the Lawesson's reagent (LR, 6a) or with the Japanese reagent (JR, 6b) in dry toluene. Upon evaluation of HIV-1 Reverse Transcriptase enzyme inhibition, compound 8b (IC50=2.93nM) exhibited the superior HIV-1 RT inhibition and its potency was about 3-folds that of Efavirenz (IC50=6.03nM). Also, compounds 9a (IC50=4.09nM) and 12 (IC50=3.54nM) showed significantly higher inhibition potency. Moreover, compounds 7b (IC50=7.48nM), and 8a (IC50=4.55nM) showed potency not significantly different from that of Efavirenz. Molecular docking experiments on these potent compounds was in accordance with the in vitro data and confirmed binding of these compounds to the enzyme through ring-stacking and hydrogen bond interactions. According to these results, the new molecules would serve as potent HIV-1 NNRTIs inhibitors.

Metabolites of the Anaerobic Degradation of n-Hexane by Denitrifying Betaproteobacterium Strain HxN1.

The constitutions of seven metabolites formed during anaerobic degradation of n‐hexane by the denitrifying betaproteobacterium strain HxN1 were elucidated by comparison of their GC and MS data with those of synthetic reference standards. The synthesis of 4‐methyloctanoic acid derivatives was accomplished by the conversion of 2‐methylhexanoyl chloride with Meldrum's acid. The β‐oxoester was reduced with NaBH4, the hydroxy group was eliminated, and the double bond was displaced to yield the methyl esters of 4‐methyl‐3‐oxooctanoate, 3‐hydroxy‐4‐methyloctanoate, (E)‐4‐methyl‐2‐octenoate, and (E)‐ and (Z)‐4‐methyl‐3‐octenoate. The methyl esters of 2‐methyl‐3‐oxohexanoate and 3‐hydroxy‐2‐methylhexanoate were similarly prepared from butanoyl chloride and Meldrum's acid. However, methyl (E)‐2‐methyl‐2‐hexenoate was prepared by Horner–Wadsworth–Emmons reaction, followed by isomerization to methyl (E)‐2‐methyl‐3‐hexenoate. This investigation, with the exception of 4‐methyl‐3‐oxooctanoate, which was not detectable in the cultures, completes the unambiguous identification of all intermediates of the anaerobic biodegradation of n‐hexane to 2‐methyl‐3‐oxohexanoyl coenzyme A (CoA), which is then thiolytically cleaved to butanoyl‐CoA and propionyl‐CoA; these two metabolites are further transformed according to established pathways.

Synthesis of Butenolides via a Horner-Wadsworth-Emmons Cascading Dimerization Reaction.

The efficient synthesis of a range of structurally related butenolides has been observed while we were exploring the substrate-scope of a Horner-Wadsworth-Emmons (HWE) reaction. While aliphatic aldehydes gave the expected HWE product, aromatic aldehydes furnished butenolides, resulting from the dimerization of the HWE product during desilylation of the initially formed HWE adduct. In addition to isolating butenolides in a high yield, we have also determined precisely when dimerization occurs.

γ‐Functionalization of α,β‐Unsaturated Nitriles under Mild Conditions: Versatile Synthesis of 4‐Aryl‐2‐Bromopyridines

AbstractThis report describes the synthesis of 4‐aryl‐2‐halopyridines via γ‐functionalization of α,β‐unsaturated nitriles, which were obtained by the HWE reaction with the corresponding ketones. The key features of our methods involve a conjugated γ‐enamine formation of α,β‐unsaturated nitrile (enamino nitrile), followed by consecutive intramolecular cyclization, resulting in heteroaromatic compounds like 2‐halopyridines, α‐pyrone, etc.magnified image