Showing papers on "Claisen rearrangement published in 2014"
TL;DR: In this paper, eugenol and bieugenol were reacted with allyl bromide in the presence of sodium hydroxide to produce allyl-etherified EG and BEG (AEG and ABEG), respectively.
59 citations
TL;DR: In this paper, a continuous-flow microwave reactor with a unique pressure control device is described, which has been designed to withstand extremely high pressure without the involvement of a conventional backpressure-creating device that commonly results in carryover and cross-contamination problems.
56 citations
TL;DR: A one-pot multistep pathway, which directly gives 2,5-dihydropyrroles starting from terminal alkynes, sulfonyl azides, and propargylic alcohols, is formulated.
Abstract: Relay actions of copper, rhodium, and gold formulate a one-pot multistep pathway, which directly gives 2,5-dihydropyrroles starting from terminal alkynes, sulfonyl azides, and propargylic alcohols. Initially, copper-catalyzed 1,3-dipolar cycloaddition of terminal alkynes with sulfonyl azides affords 1-sulfonyl-1,2,3-triazoles, which then react with propargylic alcohols under the catalysis of rhodium. The resulting alkenyl propargyl ethers subsequently undergo the thermal Claisen rearrangement to give α-allenyl-α-amino ketones. Finally, a gold catalyst prompts 5-endo cyclization to produce 2,5-dihydropyrroles.
52 citations
TL;DR: In this article, a new catalytic protocol for the synthesis of γ, δ−unsaturated carbonyl units from simple starting materials, allylic alcohols and alkynes, via a hydroxalkoxylation/Claisen rearrangement sequence was reported.
Abstract: We report a new catalytic protocol for the synthesis of γ,δ−unsaturated carbonyl units from simple starting materials, allylic alcohols and alkynes, via a hydroxalkoxylation/Claisen rearrangement sequence. This new process is more efficient (higher TON and TOF) and more eco-friendly (increased mass efficiency) than the previous state-of-the-art technique. In addition, this method tolerates both terminal and internal alkynes. Moreover, computational studies have been carried out in order to shed light on how the Claisen rearrangement is initiated.
51 citations
TL;DR: An efficient and convenient synthesis of α-allyl cyclic amidines has been achieved by applying a novel cascade reaction and an aza-Claisen rearrangement to furnish the titled amidines with complete stereocontrol.
Abstract: An efficient and convenient synthesis of α-allyl cyclic amidines has been achieved by applying a novel cascade reaction. Copper(I)-mediated in situ N-sulfonyl ketenimine formation from the reaction of a terminal alkyne with sulfonyl azide is followed by an intramolecular nucleophilic attack on the central carbon atom by an allylic tertiary amine, and then an aza-Claisen rearrangement takes place through a chair transition state to furnish the titled amidines with complete stereocontrol.
49 citations
TL;DR: The orthoester Johnson-Claisen rearrangement has been used extensively in the past four decades in the synthesis of bioactive molecules, natural products, synthetic intermediates, analogues, and useful building blocks.
41 citations
TL;DR: Asymmetric synthesis of the [5-6-7] tricyclic system common to the Calyciphylline A-type alkaloids is reported, featuring Overman rearrangement, Heck cyclization, intramolecular [3 + 2] cycloaddition, diastereoselective hydrogenation, and Claisen rearrangements as strategic events.
36 citations
TL;DR: Claisen rearrangement reaction was employed for the first time to obtain a novel PPTA bearing reactive allyl and hydroxyl groups which may act as a sizing agent of Kevlar fibers to improve the interface structure and interfacial adhesion of rubber or epoxy based composites.
34 citations
TL;DR: Biomimetic total syntheses of potent antiviral spirooliganones A and B were achieved with 3% and 2% yield, respectively, in 12 steps from commercially available materials.
33 citations
TL;DR: In this article, the allylation reaction and the aromatic Claisen rearrangement of allyl group on lignin as chemical modifications are reported for the first time in this work, aimed at the development of new Lignin-based materials and the improvement of its compatibility and ease of processing.
Abstract: The conversion of lignin into value-added products is traditionally hampered by its stochastic structure and its complex reactivity. The allylation reaction and the aromatic Claisen rearrangement of the allyl group on lignin as chemical modifications are reported for the first time in this work. This approach is aimed at the development of new lignin-based materials and the improvement of its compatibility and ease of processing. In particular, the Claisen rearrangement of lignin is foreseen as a valuable approach to release phenolic groups in an already chemically modified lignin, giving additional reactive sites for further transformation. These reactions were carried out on a purely guaiacylic lignin (TMP), taken as reference material due to its simplicity, and on a more structurally complex herbaceous lignin (P1000®). The Claisen rearrangement of the allylic chain was successfully achieved by treatment in dimethylformamide at reflux temperature for 15 hours. Finally, a screening of the antioxidant activity of reference, allylated, and Claisen rearranged lignins was carried out. Rearranged lignins exhibited satisfactory antioxidant activities if compared to the reference ones.
28 citations
TL;DR: The proposed structure of polycitorols is synthesized and it is demonstrated that the structure of these alkaloids requires revision.
Abstract: We describe a flexible and divergent route to the pyrrolo-/pyrido[1,2-j]quinoline frameworks of tricyclic marine alkaloids via a common intermediate formed by the ester-enolate Claisen rearrangement of a cyclic amino acid allylic ester. We have synthesized the proposed structure of polycitorols and demonstrated that the structure of these alkaloids requires revision. In addition to asymmetric formal syntheses, stereoselective and concise total syntheses of (-)-lepadiformine and (-)-fasicularin were also accomplished from simple, commercially available starting materials in a completely substrate-controlled manner. The key step in these total syntheses was the reagent-dependent stereoselective reductive amination of the common intermediate to yield either indolizidines 55 a or 55 b. Aziridinium-mediated carbon homologation of the hindered C-10 group to the homoallylic group facilitated the synthesis.
TL;DR: In this article, a facile double allylation/ring-closing metathesis/Claisen rearrangement route for preparing vinylcyclopropanes was developed, which includes O-allylation of α-allyl-α-sulfonylketones with allylic bromides.
TL;DR: The DABCO-catalyzed reaction of propargyl alcohols with methyl 2-perfluoroalkynoate to give trifluoromethylated furans in up to 98% yield under mild conditions has been developed and should proceed through a Michael addition and Claisen rearrangement/cyclization process.
Abstract: The DABCO-catalyzed reaction of propargyl alcohols with methyl 2-perfluoroalkynoate to give trifluoromethylated furans in up to 98% yield under mild conditions has been developed. The established allene-enol and control experiments indicate that the reaction should proceed through a Michael addition and Claisen rearrangement/cyclization process.
TL;DR: Two hydrogen bond donating groups, a phenol alcohol and a carboxylic acid, were grafted onto a conformationally restrained spirocyclic scaffold, and together they enhance the rate of the Claisen rearrangement by a factor of 58 over the background reaction.
Abstract: A series of hydrogen-bonding catalysts have been designed for the aromatic Claisen rearrangement of a 1,1-dimethylallyl coumarin. These catalysts were designed as mimics of the two-point hydrogen-bonding interaction present in ketosteroid isomerase that has been proposed to stabilize a developing negative charge on the ether oxygen in the migration of the double bond.1 Two hydrogen bond donating groups, a phenol alcohol and a carboxylic acid, were grafted onto a conformationally restrained spirocyclic scaffold, and together they enhance the rate of the Claisen rearrangement by a factor of 58 over the background reaction. Theoretical calculations correctly predict the most active catalyst and suggest that both preorganization and favorable interactions with the transition state of the reaction are responsible for the observed rate enhancement.
TL;DR: In this paper, the Suzuki coupling reaction was used to synthesize four chalcones bearing prenyl or geranyl groups, i.e., isobavachalcone (1), bavach alcones (2), xanthoangelol (3), and 2′,4′, 4-trihydroxy-5′-geranylchalcone (4), which achieved a 36% overall yield.
TL;DR: In this paper, the synthesis of seven-membered sultones fused with different carbo-and heterocycles has been developed using ring closing metathesis as the key operation.
TL;DR: An efficient and scalable total synthesis of the architecturally challenging sesquiterpenoid (±)-penifulvin A has been accomplished via a 12-step sequence with an overall yield of 16%.
TL;DR: The Ireland-Claisen rearrangement of boron ketene acetals is described, which allows for a wider substrate scope that extends to propionates and arylacetates, as well as the previously described α-oxygenated esters.
Abstract: The Ireland-Claisen rearrangement of boron ketene acetals is described. The boron ketene acetal intermediates are formed through a soft enolization that obviates the use of strong bases and the intermediacy of alkali metal enolates. Yields and diastereoselectivities of these rearrangements are very sensitive to the choice of boron reagent, even among those that have been shown to effect quantitative formation of boron ketene acetals from esters. The rearrangement occurs at room temperature for all substrates with generally high levels of stereoselectivity. In contrast to previous reports using boron triflates, the use of a commercially available boron iodide reagent allows for a wider substrate scope that extends to propionates and arylacetates, as well as the previously described α-oxygenated esters. This work also provides insight into the dynamic nature of boron ketene acetals and the ramifications of this behavior for reactions in which they are intermediates.
TL;DR: A highly stereocontrolled, convergent total synthesis of kendomycin [(-)-TAN2162], an ansa-macrocyclic antibiotic, is reported.
Abstract: A highly stereocontrolled, convergent total synthesis of kendomycin [(-)-TAN2162], an ansa-macrocyclic antibiotic, is reported. The key of the strategy is an unprecedented Tsuji-Trost macrocyclic etherification, followed by a transannular Claisen rearrangement to construct the 18-membered carbocyclic framework. The oxa-six- and five-membered rings were also stereoselectively constructed respectively by a cascade oxidative cyclization at an unfunctionalized benzylic position and using a one-pot epoxidation/5-exo-tet epoxide opening.
TL;DR: In this paper, the generation of highly substituted furans from propargyl vinyl ethers bearing a free hydroxy group was investigated, and a formal [3,3] sigmropic rearrangement took place in the first stage of the sequence.
TL;DR: In this article, a stereoselective approach for the formation of 2,8-dioxabicyclo[3.3.1]nonane/nonene frameworks through formation of 3-C-branched glycals encompassing the Claisen rearrangement of the carbohydrate-derived allyl-vinyl ethers and TMSOTf-catalyzed acetalization reactions as key steps is revealed.
TL;DR: Intricate caged molecular frameworks are assembled by an atom economical process via a Diels–Alder reaction, a Claisen rearrangement, a ring-closing metathesis (RCM), and an alkenyl Grignard addition.
Abstract: Intricate caged molecular frameworks are assembled by an atom economical process via a Diels–Alder (DA) reaction, a Claisen rearrangement, a ring-closing metathesis (RCM) and an alkenyl Grignard addition. The introduction of olefinic moieties in the pentacycloundecane (PCUD) framework at appropriate positions followed by RCM led to the formation of novel heptacyclic cage systems.
TL;DR: Findings indicate that the influence of the various substituent patterns on the rate of rearrangement in these compounds differs from that documented in the literature for the analogous [3,3]-sigmatropic rearrangements of allyl vinyl ethers.
Abstract: Kinetic investigations of substituent effects in the thermal rearrangement of bis-vinyl ether substrates are reported. Findings indicate that the influence of the various substituent patterns on the rate of rearrangement in these compounds differs from that documented in the literature for the analogous [3,3]-sigmatropic rearrangement of allyl vinyl ethers. In addition, the thermochemical data collected suggests the existence of a dissociative transition state with significant dipolar character. These findings provide a unique contribution to the already extensive body of literature dedicated to mechanistic investigation of the Claisen rearrangement of aliphatic allyl vinyl ethers.
TL;DR: The NBO analysis revealed that substitution of the methyl groups on the aliphatic segment has decreased the stabilization energy E(2) and favors the aryl propargyl ether Claisen rearrangement.
Abstract: The mechanism of aryl propargyl ether Claisen rearrangement in gas and solvent phase was investigated using DFT methods. Solvent phase calculations are carried out using N,N-diethylaniline as a solvent in the PCM model. The most favorable pathways involve a [3,3]-sigmatropic reaction followed by proton transfer in the first two steps and then deprotonation or [1,5]-sigmatropic reaction. Finally, cyclization yields benzopyran or benzofuran derivatives. The [3,3]-sigmatropic reaction is the rate-determining step for benzopyran and benzofuran with ΔG‡ value of 38.4 and 37.9 kcal mol−1 at M06/6-31+G**//B3LYP/6-31+G* level in gas and solvent phase, respectively. The computed results are in good agreement with the experimental results. Moreover, it is found that the derivatives of aryl propargyl ether proceeded Claisen rearrangement and the rate-determining step may be shifted from the [3,3]-sigmatropic reaction to the tautomerization step. The NBO analysis revealed that substitution of the methyl groups on the aliphatic segment has decreased the stabilization energy E(2) and favors the aryl propargyl ether Claisen rearrangement.
TL;DR: In this article, a new protocol based on sequential applications of three atomeconomic processes viz. Claisen rearrangement, olefin isomerisation, and ring-closing diene metathesis has been developed to access a range of linear and angularly fused pyranocoumarin derivatives.
Abstract: A new protocol based on sequential applications of three atom-economic processes viz. Claisen rearrangement, olefin isomerisation, and ring-closing diene metathesis has been developed to access a range of linear and angularly fused pyranocoumarin derivatives. Incorporation of enyne (in place of diene) metathesis and Diels–Alder reaction in the sequence has allowed the corresponding benzannulated derivatives to be prepared in good yields.
TL;DR: In this paper, N-(4-hydroxy phenyl) maleimide (HPMI) is prepared and functionalized with acryloyl, methacryl-oyl and allyl, propargyl, and cyanate groups.
Abstract: N-(4-Hydroxy phenyl) maleimide (HPMI) is prepared and is functionalized with acryloyl, methacryloyl, allyl, propargyl, and cyanate groups. The structural and thermal characterizations of the materials are done using FTIR, NMR, DSC, and TGA. Curing and degradation kinetics are performed using Flynn-Wall-Ozawa, Vyazovkin, and Friedman methods. Activation energies (Ea) for the polymerization of the synthesized monomers varied and are dependent on the nature of the functional group present in HPMI. The propargyl functionalized monomer shows the highest Ea values whereas the methacryloyl functionalized monomer shows the lowest Ea values. In the case of thermal degradation of the polymerized materials, the apparent Ea values for acryloyl, methacryloyl and cya- nate functionalized materials are slightly higher than that of poly-HPMI (PHPMI). The thermally cured allyl and propargyl function- alized materials show a different trend and may be attributed to the complications arising due to Claisen rearrangement reaction during the thermal curing. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39935.
TL;DR: The enantioselective synthesis of (-)-9,10-dihydroecklonialactone B is described, with mixed success in terms of E/Z selectivity.
Abstract: The enantioselective synthesis of (−)-9,10-dihydroecklonialactone B is described. The catalytic asymmetric Claisen rearrangement of a Gosteli-type allyl vinyl ether was utilized to afford an acyclic α-keto ester building block endowed with functionality amenable to the preparation of the carbocyclic target molecule by suitable postrearrangement transformations: A highly diastereoselective Corey–Bakshi–Shibata reduction of a β-chiral α-keto ester and a reductive homologation of an α-hydroxy ester. A transprotection tactic by a chemoselective intramolecular 6-exo-trig iodoetherification enabled regioselective ring-closing alkene metatheses to afford the 5- as well as the 14-membered ring, however, with mixed success in terms of E/Z selectivity.
TL;DR: In this paper, double Claisen rearrangement reaction and ring-closing metathesis reaction were used to obtain cyclophane derivatives with ethylene oxy bridge by using double-closest ring-closed metatheses.
TL;DR: An efficient method for the synthesis of novel medium ring phosphorus containing heterocycles starting from phenol derivatives by ruthenium catalyzed ring closing metathesis is described in this article.
TL;DR: The asymmetric synthesis of (-)-dihydrosporothriolide, a biologically active bis-γ-butyrolactone, is described, that proceeds through a D-proline-catalyzed asymmetric aminooxylation, indium-mediated Reformatsky-Claisen rearrangement of an α,α-dibromoacetate derivative, and diastereoselective dihydroxylation.
Abstract: The asymmetric synthesis of (-)-dihydrosporothriolide (1), a biologically active bis-γ-butyrolactone, is described, that proceeds through a D-proline-catalyzed asymmetric aminooxylation, indium-mediated Reformatsky-Claisen rearrangement of an α,α-dibromoacetate derivative, and diastereoselective dihydroxylation. The route requires no protective group manipulation and allows the concise seven-step synthesis of 1 from n-octanal.