Showing papers on "Claisen rearrangement published in 2016"
TL;DR: An aryne 1,2,3-trisubstitution with aryl allyl sulfoxides is accomplished, featuring an incorporation of C-S, C-O, and C-C bonds on the consecutive positions of a benzene ring.
Abstract: An aryne 1,2,3-trisubstitution with aryl allyl sulfoxides is accomplished, featuring an incorporation of C–S, C–O, and C–C bonds on the consecutive positions of a benzene ring. The reaction condition is mild with broad substrate scope. Preliminary mechanistic study suggests a cascade formal [2 + 2] reaction of aryne with S═O bond, an allyl S → O migration, and a Claisen rearrangement.
103 citations
TL;DR: The total synthesis of lundurines A–C has been accomplished in racemic and enantiopure forms in 11–13 and 12–14 steps, respectively, without protection/deprotection of functional groups.
Abstract: The total synthesis of lundurines A–C has been accomplished in racemic and enantiopure forms in 11–13 and 12–14 steps, respectively, without protection/deprotection of functional groups, by a novel tandem double condensation/Claisen rearrangement, a gold(I)-catalyzed alkyne hydroarylation, a cyclopropanation via formal [3 + 2] cycloaddition/nitrogen extrusion, and a remarkable olefin migration through a vinylcyclopropane retro-ene/ene reaction that streamlines the endgame.
80 citations
TL;DR: Total synthesis of (-)-daphenylline, a hexacyclic Daphniphyllum alkaloid, was achieved and the ABC ring system was stereoselectively constructed through intramolecular cycloaddition of the cyclic azomethine ylide.
Abstract: Total synthesis of (-)-daphenylline, a hexacyclic Daphniphyllum alkaloid, was achieved. Construction of the tricyclic DEF ring system was initiated by asymmetric Negishi coupling followed by an intramolecular Friedel-Crafts reaction. Installation of a side chain onto the tricyclic core was carried out through Sonogashira coupling, stereocontrolled Claisen rearrangement by taking advantage of the characteristic conformation of the tricyclic DEF core, and the stereoselective alkylation of a lactone. After the introduction of a glycine unit, the ABC ring system was stereoselectively constructed through intramolecular cycloaddition of the cyclic azomethine ylide.
75 citations
TL;DR: The development of a kinetic resolution and asymmetric rearrangement of racemic propargyl vinyl ethers afforded chiral allene products along with the enantiomerically enriched substrate in good yields with excellent diastereo- and enantioselectivity.
Abstract: The asymmetric propargyl Claisen rearrangement provides a convenient entry to chiral allene motifs. Herein, we describe the development of a kinetic resolution and asymmetric rearrangement of racemic propargyl vinyl ethers. This transformation afforded chiral allene products along with the enantiomerically enriched substrate in good yields with excellent diastereo- and enantioselectivity. The complete chirality transfer and facially selective rearrangement enabled the simultaneous construction of an axially chiral allenic unit and a quaternary carbon stereocenter.
65 citations
TL;DR: Metal-catalyzed, double Claisen rearrangement of a bis-allyloxyflavone has been utilized to enable a concise synthesis of the hydrobenzofuro[3,2-b]chromenone core structure of the natural products sanggenon A and sanggenol F.
Abstract: Metal-catalyzed, double Claisen rearrangement of a bis-allyloxyflavone has been utilized to enable a concise synthesis of the hydrobenzofuro[3,2-b]chromenone core structure of the natural products sanggenon A and sanggenol F. In addition, catalytic, enantioselective [4+2] cycloadditions of 2′-hydroxychalcones have been accomplished using B(OPh)3/BINOL complexes. Asymmetric syntheses of the flavonoid Diels–Alder natural products sanggenons C and O have been achieved employing a stereodivergent reaction of a racemic mixture (stereodivergent RRM) involving [4+2] cycloaddition.
48 citations
TL;DR: The enantioselective (4+2) annulation of donor-acceptor cyclobutanes and unsaturated acyl fluorides using N-heterocyclic carbene catalysis allows a 3-step synthesis of cyclohexyl β-lactones in excellent chemical yield and stereochemical integrity.
Abstract: Herein we report the enantioselective (4+2) annulation of donor–acceptor cyclobutanes and unsaturated acyl fluorides using N-heterocyclic carbene catalysis. The reaction allows a 3-step synthesis of cyclohexyl β-lactones (25 examples) in excellent chemical yield (most ≥90 %) and stereochemical integrity (all >20:1 d.r., most ≥97:3 e.r.). Mechanistic studies support ester enolate Claisen rearrangement, while derivatizations provide functionalized cyclohexenes and dihydroquinolinones.
42 citations
TL;DR: Using DFT calculations, the use of halogen bonding (XB) interactions to accelerate and control organic reactions, namely Diels-Alder reaction, Claisen rearrangement, and Cope-type hydroamination are investigated.
Abstract: Using DFT calculations, we investigated the use of halogen bonding (XB) interactions to accelerate and control organic reactions, namely Diels–Alder reaction, Claisen rearrangement, and Cope-type hydroamination. Our designed triarylbenzene tripodal organocatalyst is characterized by three halogen bond donors, perfluoro-iodophenyl groups. The calculated transition states unravel multiple halogen bonds between the iodine atoms and various types of halogen bond acceptors (lone pair, π and σ bonds). These cooperative noncovalent interactions provide efficient binding between the catalyst and substrate (∼15 kcal/mol binding energy) and are the key factors for transition-state stabilization and molecular recognition. On the basis of our DFT calculations and calculated turnover frequencies, the XB-catalyzed reactions are found to be competitive with the corresponding hydrogen bonding catalysis reported in literature.
38 citations
TL;DR: In this article, the authors demonstrate that using a [3, 3]-sigmatropic rearrangement, the temperature required for the rearrangements of a solid glassy polymer was reduced by 200°C.
Abstract: Thermally rearranged (TR) polymers, which are considered the next-generation of membrane materials because of their excellent transport properties and high thermal and chemical stability, are proven to have significant drawbacks because of the high temperature required for the rearrangement and low degree of conversion during this process. We demonstrate that using a [3,3]-sigmatropic rearrangement, the temperature required for the rearrangement of a solid glassy polymer was reduced by 200°C. Conversions of functionalized polyimide to polybenzoxazole of more than 97% were achieved. These highly mechanically stable polymers were almost five times more permeable and had more than two times higher degrees of conversion than the reference polymer treated under the same conditions. Properties of these second-generation TR polymers provide the possibility of preparing efficient polymer membranes in a form of, for example, thin-film composite membranes for various gas and liquid membrane separation applications.
30 citations
TL;DR: The SmI2 -mediated cyclization and the subsequent chemoselective reduction of a lactam moiety accomplished the first enantioselectives total synthesis of (+)-neostenine (1).
Abstract: A chirality transfer approach using acyclic polyol intermediates for the synthesis of (+)-neostenine (1) has been developed. The sequential Overman/Claisen rearrangement of an allylic 1,2-diol was especially useful, installing two contiguous stereocenters with complete diastereoselectivity in a one-pot sequence. The SmI2 -mediated cyclization and the subsequent chemoselective reduction of a lactam moiety accomplished the first enantioselective total synthesis of (+)-neostenine (1).
29 citations
TL;DR: In this paper, a series of wholly aromatic copolyamides, poly(p-phenylene terephthalamide)-ran-poly[pphenylene 2,5-diallyl−3,6-dihydroxyterephthalamides] (CRPPTA-x), were converted to the target copolymers through the Claisen rearrangement reaction, as characterized by a comprehensive analyses of NMR, FT-IR, gel permeation chromatography, and differential scanning calorimetry.
Abstract: A series of novel wholly aromatic copolyamides, poly(p-phenylene terephthalamide)-ran-poly[p-phenylene 2,5-bis(allyloxy)terephthalamide] (APPTA-x, x (=0, 5, 25, 50, 60, 75, 90, and 100) represents the molar fraction of allyloxy containing structure unit), were prepared via low temperature solution copolycondensation of p-phenylenediamine, terephthaloyl chloride, and 2,5-bis(allyloxy)terephthaloyl chloride. They were converted to the target copolymers, poly(p-phenylene terephthalamide)-ran-poly[p-phenylene 2,5-diallyl−3,6-dihydroxyterephthalamide] (CRPPTA-x), through Claisen rearrangement reaction, as characterized by a comprehensive analyses of NMR, FT-IR, gel permeation chromatography, and differential scanning calorimetry. Although APPTA-x had a poor solubility in common organic solvents, the rearranged products with high co-unit contents, that is, CRPPTA-60, 75, 90, and 100, were readily dissolved in m-cresol, DMF, DMAc, DMSO, and NMP. The effect of these four polymers, used as sizing agents, on the interfacial adhesion between Kevlar fiber and epoxy resin was investigated by the contact angle method, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and microbond tests. Compared with the naked fibers, the sized fibers displayed enhanced surface energy and roughness. The fibers sized with 0.5 wt % CRPPTA-60 solution in NMP exhibited a maximum increase of 19% in interfacial shear strength. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016
27 citations
TL;DR: A novel protocol has been successfully established for the efficient synthesis of benzothiazole-tethered chromanone/coumarin scaffolds via Claisen rearrangement using a solid state melt reaction in a one-pot manner.
Abstract: A novel protocol has been successfully established for the efficient synthesis of benzothiazole-tethered chromanone/coumarin scaffolds via Claisen rearrangement using a solid state melt reaction in a one-pot manner. Benzothiazole formation and Claisen rearrangement involve the cleavage of S–S and C–O bonds and formation of C–S, C═N, and C–C bonds in a single operation without using a catalyst or solvent.
TL;DR: The synthesis of a 6-propenyl-substituted advanced intermediate for the total synthesis of these natural products is presented and the Grubbs II-catalyzed olefin cross metathesis of the 6-allyl moiety with 2-methylbut-2-ene to afford a precursor of peniprequinolone is also reported.
Abstract: 5-Hydroxy-4-aryl-3,4-dihydro-1H-quinolin-2-ones are a small family of natural products isolated from fungal strains of Penicillium and Aspergillus. Most of its members, which are insecticides and anthelmintics, carry an isoprenoid C-6 side chain. The synthesis of a 6-propenyl-substituted advanced intermediate for the total synthesis of these natural products is presented in this paper. This was achieved through the stereoselective construction of a β,β-diarylacrylate derivative from 6-nitrosalicylaldehyde, using a Wittig olefination and a Heck-Matsuda arylation, followed by a selective Fe(0)-mediated reductive cyclization. Installation of the 6-propenyl side chain was performed by 5-O-allylation of the heterocycle, followed by Claisen rearrangement and conjugative migration of the allyl double bond, as the key steps. The Grubbs II-catalyzed olefin cross metathesis of the 6-allyl moiety with 2-methylbut-2-ene to afford a precursor of peniprequinolone is also reported.
TL;DR: In this article, the authors present a model of the Claisen rearrangement of allyl phenyl ether to cyclohexa-2,4-dien-1-one.
Abstract: The Claisen rearrangement of allyl phenyl ether to 6-(prop-2-en-1-yl) cyclohexa-2,4-dien-1-one has been studied by means of Bonding Evolution Theory (BET), which combines the topological analysis of the electron localization function (ELF) and catastrophe theory. The reaction can be presented as consisting of 10 main steps separated by fold and cusp catastrophes. The description of the mechanism of C–O bond breaking is complicated and depends on the DFT method used. It proceeds through a heterolytic cleavage (B3LYP, M052x) with the formation of the V3(O) non-bonding basin in step II (M052x) or with electron density resonating between oxygen and carbon atoms in step II (B3LYP). The C–C bond between the allyl group and the phenol ring is formed after the TS in step VIII. The reaction is terminated by the formation of two localized CC bonds in the phenyl ring in steps IX and X. The localization of Vi=1,2(C,C) basins – typical of localized double bonds – in the phenyl ring proves the process of dearomatisation. The electronic structure of the transition structure distinguishes the non-bonding electron density concentrated in the vicinity of the C2 atom, represented by the V(C2) basin, with a population of 0.28e. This basin is a “bridgehead” for the “construction” of the C–C bond between the phenyl ring and the allyl group.
TL;DR: In this paper, the microwave selective heating effects of polar reactants in homogeneous reaction mixture of intramolecular aromatic Claisen rearrangement were investigated. And the results showed direct evidence for localized superheating of polar reactsants in nonpolar solvent.
TL;DR: The synthesis of 2-allenyl-2-substituted-3,3-difluoroindolines has been accomplished, taking advantage of the reaction between N-allanyl-indoles and Selectfluor under iron catalysis.
TL;DR: The first total syntheses ofClausenapin, indizoline, claulansine M, and a novel synthetic route to clausenaline D via divergent method through TFAA-mediated intramolecular acylation and subsequent Claisen rearrangement to generate key intermediates for further elaboration to target molecules are described.
Abstract: We described the first total syntheses of clausenapin, indizoline, claulansine M, and a novel synthetic route to clausenaline D via divergent method. Key steps involved TFAA-mediated intramolecular acylation to construct the carbazole core and subsequent Claisen rearrangement to generate key intermediates for further elaboration to target molecules.
TL;DR: An efficient reductive Claisen rearrangement, catalyzed by in situ generated copper hydride and stoichiometric in diethoxymethylsilane, has been developed and it is shown that the stereospecific rearrangements proceeded via a chair transition state of (E)-silyl ketene acetals as intermediates and not via the copper enolates.
Abstract: An efficient reductive Claisen rearrangement, catalyzed by in situ generated copper hydride and stoichiometric in diethoxymethylsilane, has been developed. Yields of up to 95 % with good to excellent diastereoselectivities were observed in this reaction. Mechanistic studies showed that the stereospecific rearrangement proceeded via a chair transition state of (E)-silyl ketene acetals as intermediates and not via the copper enolates.
TL;DR: In this paper, the authors describe the development of a kinetic resolution and asymmetric rearrangement of racemic propargyl vinyl ethers, which enabled chiral allene products along with the enantiomerically enriched substrate in good yields with excellent diastereo and enantioselectivity.
Abstract: The asymmetric propargyl Claisen rearrangement provides a convenient entry to chiral allene motifs. Herein, we describe the development of a kinetic resolution and asymmetric rearrangement of racemic propargyl vinyl ethers. This transformation afforded chiral allene products along with the enantiomerically enriched substrate in good yields with excellent diastereo- and enantioselectivity. The complete chirality transfer and facially selective rearrangement enabled the simultaneous construction of an axially chiral allenic unit and a quaternary carbon stereocenter.
TL;DR: The enantioselective total synthesis of (–)-stemoamide using Overman/Claisen rearrangement of an allylic 1,2-diol is reported, and the chirality transfer reactions through two consecutive [3,3]-sigmatropic rearrangements proceeded with complete diastereoselectivity in a one-pot process.
Abstract: The enantioselective total synthesis of (–)-stemoamide using Overman/Claisen rearrangement of an allylic 1,2-diol is reported. The enantiopure allylic 1,2-diol was efficiently prepared from naturally occurring dimethyl tartrate. The chirality transfer reactions through two consecutive [3,3]-sigmatropic rearrangements proceeded with complete diastereoselectivity in a one-pot process.
TL;DR: In this article, a solvent-free approach to intensification of chemical processes is reported, in which reactions are carried out solvent free, without the need for further downstream processing, was highlighted first with a full reduction of ethyl nicotinate to ethylpiperidine-3-carboxylate under continuous flow conditions.
Abstract: A solvent-free approach to intensification of chemical processes is reported. This concept, in which reactions are carried out solvent-free, without the need for further downstream processing, was highlighted first with a full reduction of ethyl nicotinate to ethylpiperidine-3-carboxylate under continuous flow conditions. Using a small footprint reactor, a throughput of 26.4 g h–1 was achieved. Similarly, this approach was used for the telescoped two-step synthesis of 2-propyl phenol (productivity 120 g h–1) and 2-propyl cyclohexanone (productivity 30 g h–1), starting from the commercially available allyl phenol ether via Claisen rearrangement and subsequent reduction.
TL;DR: In this article, allyl aryl ethers and allyl phenol derivatives were prepared starting from commercial or synthetized phenols, and either Williamson reaction or Et 2 AlCl catalyzed Claisen rearrangement was performed to obtain the polyoxygenated molecules.
TL;DR: In this paper, a facile and efficient one-step method for the synthesis of highly active mesoporous zirconium and tin(IV) phosphate that exhibit excellent catalytic activity for photochromic bis-naphthopyran via the Claisen rearrangement has been established.
Abstract: In this work, a facile and efficient one-step method for the synthesis of highly active mesoporous zirconium and tin(IV) phosphate that exhibit excellent catalytic activity for the synthesis of photochromic bis-naphthopyran via the Claisen rearrangement has been established. The synthesized catalysts were characterized by different textural and spectroscopic techniques such as XRD, FTIR spectra, SEM, TEM and N2 adsorption–desorption at −196 °C. The surface acidity of the prepared catalysts were determined by nonaqueous potentiometric titration with n-butylamine and FTIR of chemisorbed pyridine. XRD and N2 adsorption–desorption measurements showed that, the samples have some mesoporous structure. The surface acidity measurement showed that the samples contain mixture of Lewis and Bronsted acid sites. The results showed that zirconium phosphate samples have higher surface acidities than tin phosphate samples, and the samples with Zr:P ratio 1:3 and Sn:P ratio 1:2 showed the highest surface and Bronsted acidities. The prepared catalysts showed excellent catalytic activity for the synthesis of photochromic bis-naphthopyran via the Claisen rearrangement. High yield (~99 %) with 100 % selectivity of photochromic bis-naphthopyran was obtained in shorter reaction time at room temperature. These acid catalysts may solve the problematic low yield and purification difficulties of the photochromic chromenes reported previously.
TL;DR: A short synthesis of the biologically active sesquiterpene natural product (+)‐aphanamol I in both racemic and enantiopure forms is reported, using a catalytic enantioselective conjugate addition, an oxidative radical cyclization, and a ring‐expanding Claisen rearrangement.
Abstract: A short synthesis of the biologically active sesquiterpene natural product (+)-aphanamol I in both racemic and enantiopure forms is reported. Key steps include: a catalytic enantioselective conjugate addition, an oxidative radical cyclization, and a ring-expanding Claisen rearrangement.
TL;DR: An intramolecular ketene aza-Claisen rearrangement is developed for the first time to enable the stereoselective synthesis of α-ally-α-cyano-lactams from N-allyl amino esters.
TL;DR: In this article, the use of copper triflate to efficiently catalyze a [3+2] annulation of propargylic acetates with N-alkylanilines in the presence of trimethylsilyl chloride (Me3SiCl) to produce 2,3-disubstituted indole derivatives was described.
TL;DR: A new method to synthesize γ,δ-unsaturated α-nitrogenated aldehydes in very good yields is described herein.
Abstract: A new method to synthesize γ,δ-unsaturated α-nitrogenated aldehydes in very good yields is described herein. This method involves a copper-coupling reaction between β-iodoenamide derivatives and allylic alcohols to generate β-allyloxyenamide derivatives. The latter, when heated, undergo a Claisen rearrangement and form γ,δ-unsaturated α-nitrogenated aldehydes.
TL;DR: Claisen rearrangement and subsequent aldol reaction furnished trans-decaline key intermediate, which assured a formal total synthesis of (−)-Triptophenolide and (+-Triptolide.
Abstract: Catalytic asymmetric formal synthesis of (-)-Triptophenolide and (+)-Triptolide have been achieved. Key reaction involves Palladium catalyzed asymmetric conjugate addition of aryl boronic acid to 3-methyl cyclohexe-1-none to form quaternary carbon. Claisen rearrangement and subsequent aldol reaction furnished trans-decaline key intermediate, which assured a formal total synthesis of (-)-Triptophenolide and (+)-Triptolide.
TL;DR: The first asymmetric Claisen rearrangement of allenyl vinyl ethers to access optically active β-ketoesters, containing branched 1,3-butadienyl substituted stereocenters is disclosed, yielding products with excellent enantioselectivities and high yields.
TL;DR: In this paper, the photo-Claisen rearrangement was used to convert commercial meta-substituted phenols to the allyl-based precursors via nucleophilic substitution using batch technology.
Abstract: We converted diverse commercial meta-substituted phenols to the allyl-substituted precursors via nucleophilic substitution using batch technology to allow processing these in microflow by means of the photo-Claisen rearrangement. The latter process is researched on its own, as detailed below, and also prepares the ground for a fully continuous two-step microflow synthesis, as outlined above. It is known that batch processing of electronically deactivated phenols (e.g., bearing a cyano or nitro group) has several orders of magnitude lower reactivity than their parental counterparts [1]. Thus, we here explore if the high quantum yield of microflow, yet at very short residence time, is sufficient to activate the deactivated molecules. In addition, the realization of a true orthogonal two-step flow synthesis can open the door to a large synthetic scope of our approach and possibly overcome limitations due to missing orthogonality of our previously reported thermal approach of combined nucleophilic substitution-Claisen rearrangement in microflow. Consequently, we make for our photo microflow approach an orthogonality check, as previously reported for the thermal approach, and compare both. To get a broader picture, we have investigated some major parametric sensitivities such as the irradiation intensity, the choice of solvent, the reactant concentration, and, most notably, the influence of the substitution pattern. The irradiation intensity was varied by increasing distance between a lamp and the microflow capillary. In addition, the normal photo- Claisen microflow process (at room temperature) is compared to a high-temperature photo-Claisen microflow process, to check the potential of such novel process window [2]. This is difficult to realize in batch, as the combination of strong ultraviolet (UV) irradiation and high temperature causes a high hazard potential. Yet, under microflow, this can be safely handled.