Showing papers on "Annulation published in 2000"
TL;DR: Regiospecific carbonylative annulation of o-iodophenol acetates and acetylenes mediated by palladium-thiourea-dppp complex in the presence of base at 40 degrees C under a balloon pressure of CO generates diversified flavones in high yields.
188 citations
TL;DR: A highly effective cocatalysis system (PdI2-thiourea and CBr4) was developed for carbonylative cyclization of both electron-rich and electron-deficient o-hydroxylarylacetylenes to the corresponding methyl benzo[b]furan-3-carboxylates.
126 citations
TL;DR: A new strategy for enantiospecific construction of the Securinega alkaloids has been developed and applied in total syntheses of (+)-14,15-dihydronorsecurinine (8), (-)-norsecur inine (6), and phyllanthine.
Abstract: A new strategy for enantiospecific construction of the Securinega alkaloids has been developed and applied in total syntheses of (+)-14,15-dihydronorsecurinine (8), (−)-norsecurinine (6), and phyllanthine (2). The B-ring and C7 absolute stereochemistry of these biologically active alkaloids originated from trans-4-hydroxy-l-proline (10), which was converted to ketonitrile 13 via a high-yielding eight-step sequence. Treatment of this ketonitrile with SmI2 afforded the 6-azabicyclo[3.2.1]octane B/C-ring system 14, which is a key advanced intermediate for all three synthetic targets. Annulation of the A-ring of (−)-norsecurinine (6) with the required C2 configuration via an N-acyliminium ion alkylation was accomplished using radical-based amide oxidation methodology developed in these laboratories as a key step, providing tricycle 33. Annulation of the D-ring onto α-hydroxyketone 33 with the Bestmann ylide 45 at 12 kbar gave (+)-14,15-dihydronorsecurinine (8). In the securinine series, the D-ring was incorpo...
92 citations
TL;DR: In this article, an all-carbon dipole derived by the interaction of triphenylphosphine with allenic ester is able to locate the polarized 2π-component in 3-formylchromones through a regioselective [2 + 3] addition to the C2−C3 π-bond, which is followed by deformylation leading to novel 3a,9a-dihydro-1-ethoxycarbonyl-1 -cyclopenteno[5,4-b]benzopyran-4
89 citations
TL;DR: The specific formation of (Z)-isomers from Horner–Wadsworth–Emmons reaction of phosphonylglycinates and 2-iodobenzaldehydes was crucial to the success of the process and the product N-substituted indole-2-carboxylates were isolated in high yield.
71 citations
TL;DR: In this article, the nickel-catalyzed annulations of electron-deficient allenes proceed efficiently in a highly regioselective manner under very mild conditions to give the head-to-head cyclodimerization products, bismethylenecyclobutanes, as single isomers in good to fair yields.
Abstract: The nickel-catalyzed [2 + 2] annulations of electron-deficient allenes proceed efficiently in a highly regioselective manner under very mild conditions to give the head-to-head cyclodimerization products, bismethylenecyclobutanes, as single isomers in good to fair yields. We also carried out the stoichiometric reaction of these allenes in the presence of Ni(0) complexes and elucidated the mechanism of this highly selective reaction.
59 citations
TL;DR: Benzene-1,2-diol reacts with various propargylic carbonates in the presence of a palladium catalyst and a chiral atropoisomeric diphosphine to give 2-alkylidene-3,alkyl,1,4-benzodioxanes in good yields and 56-97% enantiomeric excess.
58 citations
TL;DR: The reaction was applied to the preparation of the COX-2 specific inhibitor 5-chloro-3-(4-methylsulfonyl)phenyl-2-(2-methyl-5-pyridinyl)pyridine (1), as well as a series of analogues.
57 citations
TL;DR: The reactions of the radicals derived from indoles 4 are described leading to a short synthesis of fused [1,2-a]indoles via radical addition to the benzene ring followed by rearomatisation whilst one example undergoes an unusual radical translocation/addition reaction.
TL;DR: An efficient solid-phase approach has been developed to prepare nitrogen heterocycles with a 1,2,3,4-tetrahydro-2-pyridone core via aza-annulation of enamines via acolysis of primary amines with propynoic acid derivatives or ketones.
Abstract: An efficient solid-phase approach has been developed to prepare nitrogen heterocycles with a 1,2,3,4-tetrahydro-2-pyridone core via aza-annulation of enamines Immobilized enamines were prepared from the reaction of primary amines with propynoic acid derivatives or ketones Aza-annulation reactions were carried out by reacting resin-bound enamines with symmetrical alpha,beta-unsaturated acid anhydrides or alpha,beta-unsaturated acids in the presence of DPPA and TEA The annulation products were isolated in good to high crude yields Influence of sterically hindered amines as well as alpha- and beta-substituted acrylic acid derivatives on the annulation reaction was also investigated
TL;DR: The tricyclic core of cyathins has been synthesized using a Brook rearrangement-mediated [3 + 4] annulation that was previously developed.
TL;DR: In double stereodifferentiating reactions with in situ generated imines, good levels of selectivity were achieved in the formation of secondary amines bearing syn–anti and syn–syn stereochemical triads.
TL;DR: In this paper, β-Diketones, β-ketoesters and β -ketonitriles in the presence of propargyl bromide, DBU and a catalytic amount of CuI in toluene give 2,3,5-trisubstituted furans through sequential alkylation/cyclisation/isomerisation reactions.
TL;DR: The benzhydryldimethylsilyl group has been used for annulation reactions of carbocycles and heterocycles with high stereoselectivities as discussed by the authors, and it has been shown to provide a variety of highly substituted five-membered carbocycocycicles and heterocyclic compounds.
TL;DR: A protocol has been developed in which annulation reactions of various dihalides with keto esters can be carried out to provide entry to eight- and nine-membered carbocycles.
Abstract: A protocol has been developed in which annulation reactions of various dihalides with keto esters can be carried out to provide entry to eight- and nine-membered carbocycles. In this process wherein one alkenyl- or aryl bromide and a tethered alkyl chloride comprise the organic dihalide, a selective metal−halogen exchange reaction between the sp2-hybridized bromide and an organolithium initiates the process. Transmetalation to an organoytterbium reagent generates a species that undergoes selective carbonyl addition to the ketone of the keto ester, creating a lactone intermediate. Subjection of the resulting chloroalkyl lactone to intramolecular reductive coupling with samarium(II) iodide completes the desired annulation.
TL;DR: The 4 + 1 radical annulation reaction of aryl isonitrile with iodoalkynes or iodonitriles affording cyclopenta-fused pyridines and pyrazines is described in this paper.
Abstract: The 4 + 1 radical annulation reaction of vinyl isonitriles with iodoalkynes or iodonitriles affording cyclopenta-fused pyridines and pyrazines respectively and the first example of an intramolecular radical addition to an aryl isonitrile are described.
TL;DR: In this article, aldehydes with 2-substituted 2-alkenals are formed 2,4-disubstitized 1-naphthols and/or 1,3-dissubstitized naphthalenes accompanied by decarbonylation.
TL;DR: In this article, nonconjugated aromatic hexa-and heptaynes underwent domino thermal radical cycloaromatization at 25°C to yield indenol ring-fused fluoranthene skeletons with helicity.
TL;DR: Palladium-catalysed regio- and stereoselective annulation of allenyl stannanes by β-iodo vinylic acids gives the corresponding α-pyrones in high yields.
TL;DR: An improved cascade radical annulation route to (+/-)-mappicine, (S)-mappy, and mappicines ketone analogues is reported, illustrative of how late stage cascade reactions can be employed strategically to generate libraries of polycyclic natural product analogues.
Abstract: An improved cascade radical annulation route to (±)-mappicine, (S)-mappicine, and mappicine ketone is reported. The route is used to prepare libraries of mappicine and mappicine ketone analogues in a semiautomated fashion. Key diversity generating steps include the addition of an aldehyde to a Grignard reagent derived from a D-ring iodopyridine, N-propargylation of a subsequently derived iodopyridone, and cascade radical annulation with an isonitrile to form a mappicine analogue. Parallel oxidation of mappicine analogues produced mappicine ketones. The route is general and flexible and could be used to make very large libraries. It is also illustrative of how late stage cascade reactions can be employed strategically to generate libraries of polycyclic natural product analogues.
TL;DR: The formal synthesis of the alkaloid (+/-)-peduncularine (1) was accomplished through the use of a [3 + 2] allylic silane annulation as discussed by the authors.
TL;DR: In this paper, the pKa values have been determined by spectrophotometric measurements in order to provide a basis for the understanding of the proton transfer processes in CcO.
Abstract: All three isomers of 1-(o-hydroxyphenyl)imidazole carboxylic esters (1–3) have been synthesized regioselectively via their methyl ether precursors. Methyl 1-(o-methoxyphenyl)imidazole-2-carboxylate (6) and the corresponding 1,4-isomer (11) were synthesized via Cu-catalyzed coupling of 2-iodoanisole with imidazole followed by methoxycarbonylation, and by direct coupling of 2-iodoanisole with methyl imidazole-4-carboxylate (7), respectively. The 1,5-isomer (15) was prepared by annulation of an N-aryl glycine ester derivative (13). The boron tribromide mediated cleavage of methyl ethers gave the hydroxyphenyl compounds (1–3) in good to excellent yields. These compounds can serve as building blocks for synthesizing a new generation of active-site model compounds of cytochrome c oxidase (CcO). The pKa values have been determined by spectrophotometric measurements in order to provide a basis for the understanding of the proton transfer processes in CcO.
TL;DR: In this article, a palladium catalyst and a chiral atropoisomeric diphosphine were used to give 2-alkylidene-3-alkyldene-1,4-benzodioxanes in good yi...
Abstract: Benzene-1,2-diol reacts with various propargylic carbonates in the presence of a palladium catalyst and a chiral atropoisomeric diphosphine to give 2-alkylidene-3-alkyl-1,4-benzodioxanes in good yi...
TL;DR: High regioselectivity for the annulation of 7 with nonsymmetrical diarylalkynes was observed with the selectivity controlled mainly by electronic factors rather than by steric factors.
Abstract: The reaction of diethyl 2,2‘-diiodo-4,4‘-biphenyldicarboxylate (7) with diarylacetylenes in the presence of 3,5-(NO2)2C6H3CO2Me (MeDNB) or 4-(NO2)C6H4CO2Me (MePNB), Pd(OAc)2 (10 mol %), K2CO3, and Bu4NBr, in DMF at 100 °C, gives 4-methyl-9,10-diaryl-2,7-phenanthrenedicarboxylic acid diethyl esters in good yields. The methyl group at position 4 originates from the electron-deficient methyl nitrobenzoates. High regioselectivity for the annulation of 7 with nonsymmetrical diarylalkynes was observed with the selectivity controlled mainly by electronic factors rather than by steric factors. A competitive kinetic isotope study was carried out using a 1:1 mixture of MePNB and MePNB-d3 in the annulation reaction of 7 which gave 4-methyl- and 4-(methyl-d3)phenanthrene in a 67:33 ratio, leading to an apparent value of kH/kD = 1.26. Possible mechanisms for the methyl transferring process are discussed.
TL;DR: In this article, an ab initio gas-phase analysis of triisopropylallylsilane with different ligands on the metal and on the reaction between these allylsilanes and acrolein, acrylic acid, and methyl acrylate was performed.
Abstract: Trimethylallylsilane has been shown to add to methyl acrylate in good yield when catalyzed by TiCl(4) at room-temperature despite literature reporting to the contrary. Further, even with these small alkyl ligands on the metal, ring annulation occurs to a large extent, in addition to simple allylation (Sakurai addition). The kinetic product is the ((trimethylsilyl)methyl)cyclobutane derivative which can be isomerized to cyclopentanoid, the thermodynamic product, if left in the presence of the catalyst. Consistent with other literature in this area, increasing the size of the ligands on silicon increases both the rate of product formation and the proportion of ring annulation relative to allylation. To develop a predictive model for allylsilane reactivity, ab initio gas-phase calculations have been made on the parent allylsilane with different ligands on the metal and on the reaction between these allylsilanes and acrolein, acrylic acid, and methyl acrylate. Predictions indicate that as the length of n-alkyl ligands on silicon increase, so does the apparent ability of the Si-Calpha bond of the allylsilane to hyperconjugate with developing vacant p orbital on Cbeta as the allylsilane begins to attack an electrophile. This is corroborated by a gradually increasing HOMO in the ground-state allylsilane as the ligands are changed from methyl through to n-hexyl and an increasing Si-Calpha bond length and decreasing Si-Calpha-Cbeta bond angle in the protonated species. These results in the gas phase mirror the reactivity of these n-alkyl-substituted allylsilanes in experiment; i.e., as the length of the alkyl chain increases, reactivity increases significantly. Triisopropylallylsilane, a very reactive silane, appears to anomalous in charge distribution and geometrical features compared with other substituted allylsilane systems which is due, presumably, to steric effects. The calculations on the protonated species would indicate that almost no hyperconjugative stabilization can occur on the basis of the bond lengths and angles necessary to promote good orbital overlap between the Si-Calpha bond and the empty p orbital on Cbeta. However, the gas-phase reaction of the triisopropylallylsilane with acrolein and methyl acrylate led to comparatively low energy barriers of 13.1 and 24.5, respectively, which is consistent with its high experimental reactivity. Together, this computational analysis has produced a useful model for predicting allylsilane reactivity and some possible explanations for this reactivity.