Showing papers on "Claisen rearrangement published in 2000"
TL;DR: In this paper, a biomimetic cyclization of simple isoprenoids to polycyclic isopsrenoids using Lewis acid-assisted chiral Bronsted acids, called chiral LBAs, is described.
Abstract: Syntheses of polycyclic isoprenoids have been achieved by several groups; however, no general “biomimetic” method has yet been reported In this paper we describe the biomimetic cyclization of simple isoprenoids to polycyclic isoprenoids using Lewis acid-assisted chiral Bronsted acids, “chiral LBAs” This is the first example of a proton-induced enantioselective ene cyclization in synthetic chemistry Geranyl phenyl ethers, o-geranylphenols, and geranylacetone derivatives were directly cyclized at −78 °C in the presence of (R)-binaphthol derivatives and tin tetrachloride During the cyclization, [1,3] abnormal Claisen rearrangement often took place The enantioselectivities were up to 90% ee Compounds bearing a farnesyl group could also be cyclized under the same conditions to give the natural products (−)-Ambrox and (−)-chromazonarol These chiral LBAs recognize a trisubstituted terminal olefin enantiotopically and generate site-selective carbocations on the substrates The absolute stereochemistry of t
97 citations
TL;DR: The tricycloillicinone synthesis employed a novel strategy to control the regiochemistry of two ortho Claisen rearrangements, which effectively suppressed its unwanted rearrangement to the para position.
Abstract: Tricycloillicinone (1) and bicycloillicinone asaronacetal (2) were both isolated from extracts of the wood of Illicium tashiroi. These compounds were found to enhance the action of choline acetyltransferase, which catalyzes the synthesis of acetylcholine from its precursor. Since one of the characteristic symptoms of Alzheimer's disease involves degeneration of cholinergic neurons, resulting in markedly reduced levels of acetylcholine, compounds with the properties of 1 or 2 could well serve as agents in the treatment of such disorders. In this paper, we report the total synthesis of 1 and the construction of the core structure 3 of 2. The tricycloillicinone synthesis employed a novel strategy to control the regiochemistry of two ortho Claisen rearrangements. A sulfonyl group introduced at C2 of an allyl group effectively suppressed its unwanted rearrangement to the para position (23 → 24). Subsequently, ortho Claisen rearrangement was conducted using a reverse O-prenylated derivative 31 to furnish the de...
63 citations
TL;DR: In this paper, the total synthesis of (S,R, R,R,R,R)-Nebivolol, a hypertensive agent, was reported, which consisted of Claisen rearrangement and a one-pot Sharpless asymmetric epoxidation, intramolecular epoxide opening with internal phenoxide anion to generate the chiral chromane.
60 citations
TL;DR: P-TsOH-catalyzed condensation reactions of 1,1-diaryl-2-propyn-1-ol and 2-naphthol in the solid state gave 3, 3-d Diaryl-3H- naphtho[2, 1-b]pyran (6) via Claisen rearrangement.
54 citations
TL;DR: A variety of β-C -glycosides may be readily accessed in a stereoselective fashion from 3-OH glycal esters, via the use of Tebbe methylenation and subsequent thermal Claisen rearrangement.
44 citations
TL;DR: In this paper, the Hammond postulate is used to rationalize variations in free energies of activation for different cycloadditions as a function of allyl electrophilicity.
43 citations
TL;DR: Iridium complexes were found to promote the conversion of allyl homoallyl ethers to gamma,delta-unsaturated carbonyl compounds and presumably proceeds through double bond migration to allyl vinyl ethers, which then undergo the Claisen rearrangement.
43 citations
TL;DR: Complete chirality transfer occurs in the smooth Claisen rearrangement of the trimethylsilyl ketene acetals, which were prepared from allylic malonates (R)-1 (R=pentyl, 2-(Z)-pentenyl).
Abstract: Complete chirality transfer occurs in the smooth Claisen rearrangement of the trimethylsilyl (TMS) ketene acetals, which were prepared from allylic malonates (R)-1 (R=pentyl, 2-(Z)-pentenyl). These are in turn accessible by enantioselective reduction/esterification or by enzymatic kinetic resolution. The cis configuration in (+)-3 was achieved by highly syn-selective epoxidation of (+)-2, followed by suprafacial 1,2-H migration.
42 citations
TL;DR: In this article, the utility of ionic liquids as a safe recyclable reaction at 200 °C in the presence of anhydrous scandium======trifluoromethanesulfonate for a sequential reaction involving a Claisen rearrangement and cyclizations is described.
40 citations
TL;DR: The benzofuranone 2, a potential intermediate for the synthesis of the marine natural product diazonamide A 1, has been synthesised in eight steps from the N -protected tyrosine ester 3.
40 citations
TL;DR: The oxazole substituted 4-aryltryptamine 5, a potential intermediate for the synthesis of the marine natural product diazonamide A 1, has been synthesised.
TL;DR: In this paper, the solvent effects for a Claisen rearrangement and a Diels-Alder reaction were investigated in terms of the locations and magnitudes of the curvature peaks along the reaction path, as well as the shape of the potential energy near the reaction coordinate near the transition state.
Abstract: The solvent effects for a Claisen rearrangement and a Diels-Alder reaction are investigated. Electronic structure methods are used to generate the frequencies, couplings, and curvatures along the minimum energy paths for these reactions in the gas phase and in the presence of two water molecules. The geometries and charge distributions along the minimum energy paths are analyzed to determine the structural and electrostatic roles of the water molecules. Reactive flux molecular dynamics methods based on a reaction path Hamiltonian are used to calculate the dynamical transmission coefficients, which account for recrossings of the transition state. The transmission coefficients for the Claisen rearrangement are nearly unity both in the gas phase and in the presence of two water molecules. The transmission coefficients for the Diels-Alder reaction are 0.95 and 0.89 in the gas phase and in the presence of two water molecules, respectively. These differences in the transmission coefficients are explained in terms of the locations and magnitudes of the curvature peaks along the reaction path, as well as the shape of the potential energy along the reaction coordinate near the transition state. Analysis of the dynamical trajectories provides insight into the dynamical role of the water molecules and elucidates possible reaction mechanisms.
TL;DR: In this article, the diallyl ethers of bisphenol A (APP), 4,4′-dihydroxy biphenyl (ABP), and bisphensol sulfone (ABS) were synthesized and the kinetics of their thermal rearrangement to the Diallyl Bisphenols were studied by DSC, showing that the rearrangements are disfavoured by the electron-withdrawing substituent and favored by electron-releasing groups at the para position of the allyloxy group.
TL;DR: In this paper, an endothermic Lewis acid-assisted metalla−Claisen rearrangement was found to be the key stage of the reaction for a combination of various metals including lithium, magnesium, zinc, and tin.
Abstract: The addition of an allylzinc compound to a vinylmetal compound takes place rapidly and in high yield to produce a 1,1-dimetallic organometallic species. This reaction has apparent kinetic and thermodynamic problems, and in addition, the nature of the true final product has not been known. Density functional (B3LYP) studies on this reaction for a combination of various metals including lithium, magnesium, zinc, and tin provided the first information on these unresolved issues. The key stage of the reaction was found to be an endothermic Lewis acid-assisted metalla−Claisen rearrangement that also shows some character of metallo−ene reaction of the vinylmagnesium species. The kinetic barrier of the C−C bond-forming step is quite low and the thermodynamic driving force of the reaction is provided by oligomerization of the initial product that occurs after the C−C bond formation. The high level of diastereoselectivity observed experimentally has been ascribed to the short length of the forming C−C bond in the ...
TL;DR: The X-ray crystal structure of 43 was determined to prove the stereochemistry of Triene 5, and the successful route involved conversion of 22 into the vinyl ether 23 by Petasis olefination, followed by Claisen rearrangement.
Abstract: Triene 5 has been prepared by the E-selective olefination of aldehyde 12 with the ylide 11. Several alternative syntheses of 12 were evaluated, and the successful route involved conversion of 22 into the vinyl ether 23 by Petasis olefination, followed by Claisen rearrangement. Diels−Alder cycloaddition of 5 with 4 gave the adduct 6 in 77% yield, and Reformatsky cyclization under dilution conditions afforded 10 (67%). After conversion to enol silane 32, oxidation with dimethyldioxirane produced 34. Conversion to a key intermediate 38 using electrophilic selenenylation and selenoxide rearrangement, followed by enolate alkylation and deprotection, gave 43. The X-ray crystal structure of 43 was determined to prove the stereochemistry.
TL;DR: In this article, a fully functionalized isocoumarin moiety of DNA helicase inhibitor heliquinomycin was synthesized using a modified condensation reaction of diethyl bromomalonate with readily accessible phthalaldehydic acid derivative.
TL;DR: Prephenate is the product of a Claisen rearrangement of chorismate that accelerates the reaction by a factor of 106 and the standard method for quantifyi...
Abstract: Prephenate is the product of a Claisen rearrangement of chorismate. The enzyme chorismate mutase (CM from B. subtilis) accelerates the reaction by a factor of 106. The standard method for quantifyi...
TL;DR: The total synthesis of (+)-pinguisenol, a sesquiterpene containing a cis-1,2,6,7-tetramethylbicyclo[4.0]nonane carbon framework incorporating two vicinal quaternary carbon atoms and four cis-oriented methyl groups on four contiguous carbon atoms, isolated from a liverwort, is described in this article.
Abstract: Enantiospecific total synthesis of (+)-pinguisenol 1, a sesquiterpene containing a cis-1,2,6,7-tetramethylbicyclo[4.3.0]nonane carbon framework incorporating two vicinal quaternary carbon atoms and four cis-oriented methyl groups on four contiguous carbon atoms, isolated from a liverwort, is described. The orthoester Claisen rearrangement of the allyl alcohol 9, obtained from (R)-carvone, generates the ester 12. Intramolecular cyclopropanation of the diazo ketone 13, derived from the ester 12, furnishes the tricyclic ketone 7. Degradation of the isopropenyl group followed by regioselective reductive cyclopropane ring cleavage transforms compound 7 into the hydroxy ketone 21. Wolff–Kishner reduction of the hydroxy ketone 21 followed by oxidation and Grignard reaction furnishes pinguisenol (+)-1.
TL;DR: The one-pot thermal reaction of 1,3-bis(o-acylamino phenyloxy)-2-methylene propane derivatives gave either the bis(benzoxazole) derivatives or the benzodihydrofuran derivatives via tandem Claisen rearrangement in good yields.
TL;DR: In this paper, the authors describe the synthesis of indole analogues of mycophenolic acid, which involved both the Et2O·BF3 catalyzed amino-Claisen rearrangement of N-allylindoline to 7-ally lindoline and the ortho ester Claisen rearranging of the allylic alcohol 12 to the methyl ester 14.
TL;DR: In this paper, a variety of transformations of 6-hydroxyazulenes, such as substitution of the corresponding sulfonates with nitrogen, oxygen, sulfur, carbon nucleophiles and halogens, and the Claisen rearrangement of allylic ethers, is reported.
TL;DR: A Claisen rearrangement based methodology for spiroannulation of a cyclopentane ring to cyclic precursors and its application in the formal total synthesis of acorones was described in this paper.
TL;DR: The synthesis of 2,3-dideoxy-3-C-(hydroxymethyl)-3- C-methyl-D-glycero-tetrofuranosyl++ + nucleosides was accomplished in high enatiomeric purity via [3,3]-sigmatropic Claisen rearrangement of (E)(S)-5-benzyloxy-1-tert-butyldimethylsilanyloxy-4-methyl
TL;DR: Bis(2-hydroxynaphthamide) derivatives have been synthesized via tandem Claisen rearrangement in high yields and are found to make complexes with anions and emit luminescence, serving as anion sensing fluorophores.
Abstract: Bis(2-hydroxynaphthamide) derivatives have been synthesized via tandem Claisen rearrangement in high yields. These compounds are found to make complexes with anions and emit luminescence, serving as anion sensing fluorophores.
TL;DR: In this article, the N-Boc-2-alcenyloxazolidines can be either hydrolyzed to afford enantiomerically enriched enals or further epoxidized using a two-step sequence.
TL;DR: The scope and limitations of a tandem 5-exo dig cyclization/Claisen rearrangement sequence involving appropriately substituted 4-alkyn-1-ols as an efficient "one-pot" route to fused tricyclic ring systems is described.
TL;DR: In this paper, an enantioselective approach to construction of the complex framework of CP compounds is presented, where the synthesis relies on initial elaboration of the two sidechains, and the "upper" appendage was asymmetrically dihydroxylated with both AD-mix reagents in order to lend flexibility to the scheme and provide the necessary handle for evolving the additional stereogenic centers.
Abstract: An enantioselective approach to construction of the complex framework of the CP compounds is presented. The synthesis relies on initial elaboration of the two sidechains. The "upper" appendage was asymmetrically dihydroxylated with both AD-mix reagents in order to lend flexibility to the scheme and provide the necessary handle for evolving the additional stereogenic centers. These fragments were linked to benzoic acid via Birch reduction-alkylation and subsequent cuprate addition. A series of functionalization reactions including dissolving metal reduction, Claisen rearrangement, iodolactonization, regioselective epoxide cleavage-oxidation, and intramolecular Wadsworth-Emmons cyclization took advantage of highly efficient stereocontrol. However, this flexibility was thwarted when deprotonation of a penultimate intermediate failed to be regioselective in the proper direction.
TL;DR: 3-Epi-6,7-dideoxyxestobergsterol A is synthesized from dehydroepiandrosterone in 15 steps and the key synthetic intermediate, 15 beta,16alpha-dioxypregn-17(20)E-ene derivative 8, was prepared from the corresponding 15beta,16beta-epoxide 6 by treating with acetic acid and titanium tetraisopropoxide.
Abstract: 3-Epi-6, 7-dideoxyxestobergsterol A (2), an analogue of xestobergsterol A, has been synthesized from dehydroepiandrosterone (3) in 15 steps The key synthetic intermediate, 15β, 16α-dioxypregn-17(20)E-ene derivative 8, was prepared from the corresponding 15β, 16β-epoxide 6 by reating with acetic acid and titanium tetraisopropoxide The 23-oxo side chain was constructed stereoselectively by orthoester Claisen rearrangement of 8 followed by introduction of an isobutyl group Basic treatment of the 15, 23-diketone 12 followed by deprotection gave the title compound 2