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Showing papers on "Annulation published in 2004"


Journal ArticleDOI
TL;DR: An efficient and remarkably general method for the synthesis of cyclic alkenyl ethers via the Cu(I)-catalyzed intramolecular cyclization of O-alkynylbenzaldehydes has been developed.
Abstract: An efficient and remarkably general method for the synthesis of cyclic alkenyl ethers via the Cu(I)-catalyzed intramolecular cyclization of O-alkynylbenzaldehydes has been developed. The survey of metal catalysts and solvents revealed that the combination of copper(I) iodide and DMF was the catalytic system of choice. The reaction most probably proceeds via the nucleophilic addition of alcohols 2 to O-alkynylbenzaldehydes 1 to generate the corresponding hemiacetals, and subsequent nucleophilic attack of the hemiacetal oxygen to the copper coordinated alkyne would give the annulation products 3. In all cases, the reaction proceeded in a regiospecific manner leading to the six-membered endocyclic products via 6-endo-dig cyclization.

143 citations



Journal ArticleDOI
TL;DR: The synthesis has been accomplished using a highly diastereo- and enantioselective [4 + 2] annulation for the assembly of the functionalized pyran core using an underdeveloped lactonization method involving an NaH promoted transesterification of an advanced intermediate bearing aryl cyanomethyl ester.
Abstract: Complete details of an asymmetric synthesis of apicularen (1) are described. The synthesis has been accomplished using a highly diastereo- and enantioselective [4 + 2] annulation for the assembly of the functionalized pyran core. An underdeveloped lactonization method involving an NaH promoted transesterification of an advanced intermediate bearing an aryl cyanomethyl ester was used for the macrolactonization step.

117 citations


Journal ArticleDOI
TL;DR: The palladium-catalyzed annulation of internal alkynes by N-substituted o-iodoanilines under 1 atm of carbon monoxide results in the formation of 3,4-disubstituting 2-quinolones.
Abstract: The palladium-catalyzed annulation of internal alkynes by N-substituted o-iodoanilines under 1 atm of carbon monoxide results in the formation of 3,4-disubstituted 2-quinolones. The nature of the substituent on the nitrogen is crucial to obtaining high yields of 2-quinolones. The best results are obtained using alkoxycarbonyl, p-tolylsulfonyl, and trifluoroacetyl substituents. The nitrogen substituent is lost during the course of the reaction resulting in the formation of N-unsubstituted 2-quinolones. A variety of internal alkynes, bearing alkyl, aryl, heteroaryl, hydroxyl, and alkoxyl substituents, are effective in this process. Electron-rich and electron-poor N-substituted o-iodoanilines, as well as heterocyclic analogues, can be employed as annulating agents.

112 citations


Journal ArticleDOI
TL;DR: A mild protocol for the synthesis of cis-aziridines is described that employs a catalytic amount of Brønsted acid and high levels of relative stereocontrol are also possible when forming the Schiff base from a chiral nonracemic aldehyde.
Abstract: A mild protocol for the synthesis of cis-aziridines is described that employs a catalytic amount of Bronsted acid. Despite the potential for diazo compound decomposition via alkylation or homocoupling upon exposure to a proton source, these pathways are slow relative to [2 + 1] annulation in the presence of a Schiff base, leading to aziridine product. The process uses no metals or reagents that must be removed chromatographically, exhibits rapid turnover rates, and produces only atomic nitrogen as a coproduct. High levels of relative stereocontrol are also possible when forming the Schiff base from a chiral nonracemic aldehyde.

108 citations


Journal ArticleDOI
01 May 2004-Synlett
TL;DR: In this article, a sequential condensation/annulation reaction of 2-aminoaryl ketones and α-methylene ketones using a catalytic amount of bismuth triflate is described.
Abstract: Polysubstituted quinolines are readily prepared in high yields under extremely mild conditions through a sequential condensation/annulation reaction of 2-aminoaryl ketones and α-methylene ketones using a catalytic amount of bismuth triflate.

87 citations


Journal ArticleDOI
TL;DR: In this paper, pyrene-fused porphyrins via the oxidative intramolecular ring closure reactions of meso-pyrenylporphyrin were prepared.
Abstract: We prepared novel pyrene-fused porphyrins via the oxidative intramolecular ring closure reactions of meso-pyrenylporphyrin. The excitation energies and the oxidation potentials of the isolated dark...

80 citations


Journal ArticleDOI
TL;DR: A "ring expansion-annulation strategy" for the synthesis of substituted azulenes is described based on the reaction of beta'-bromo-alpha-diazo ketones with rhodium carboxylates and the preparation of the azulenyl amino acid derivative 110.
Abstract: A “ring expansion-annulation strategy” for the synthesis of substituted azulenes is described based on the reaction of β‘-bromo-α-diazo ketones with rhodium carboxylates. The key transformation involves an intramolecular Buchner reaction followed by β-elimination of bromide, tautomerization, and in situ trapping of the resulting 1-hydroxyazulene as a carboxylate or triflate ester. Further synthetic elaboration of the azulenyl halide and sulfonate annulation products can be achieved by employing Heck, Negishi, Stille, and Suzuki coupling reactions. Reaction of the azulenyl triflate 84 with pinacolborane provides access to the azulenylboronate 91, which participates in Suzuki coupling reactions with alkenyl and aryl iodides. The application of these coupling reactions to the synthesis of biazulenes, terazulene 101, and related oligoazulenes is described, as well as the preparation of the azulenyl amino acid derivative 110.

73 citations


Journal ArticleDOI
Youhong Hu, Kenneth J. Nawoschik1, Yun Liao1, Jian Ma1, Reza Fathi1, Zhen Yang1 
TL;DR: The palladium/bpy-catalyzed annulation of o-alkynylphenol with various aryl halides to generate diversified 2,3-diarylbenzo[b]furan is described, which provides an efficient synthetic pathway for the combinatorial synthesis of conformationally restricted 2, 3-Diaryl Benzofuran for drug discovery.
Abstract: The palladium/bpy-catalyzed annulation of o-alkynylphenol with various aryl halides to generate diversified 2,3-diarylbenzo[b]furan is herein described. This method provides an efficient synthetic pathway for the combinatorial synthesis of conformationally restricted 2,3-diarylbenzo[b]furan for drug discovery.

70 citations


Journal ArticleDOI
TL;DR: Interestingly, the reaction of trifluoromethylated alkynes bearing a benzylic substituent afforded 2- or 3-trifluoroethylated indole derivatives in good yields.
Abstract: Treatment of various types of fluoroalkylated alkynes with o-iodoaniline in the presence of Pd(PPh3)4 in DMF at 80 °C for 8 h mainly gave 2-fluoroalkylated indoles in high yields. The use of P(o-Tol)3 instead of PPh3 as a ligand led to the preferential formation of 3-fluoroalkylated indoles in high yields. Interestingly, the reaction of trifluoromethylated alkynes bearing a benzylic substituent afforded 2- or 3-trifluoroethylated indole derivatives in good yields.

63 citations


Journal ArticleDOI
TL;DR: The preparation of annulated furan systems as key synthetic intermediates through the application of a two-step annulation involving an electrochemical ring closure between a furan and a silyl enol ether has been studied.
Abstract: The preparation of annulated furan systems as key synthetic intermediates through the application of a two-step annulation involving an electrochemical ring closure between a furan and a silyl enol ether has been studied. The reaction was shown to be quite general for the formation of six-membered rings in good yields and was tolerant of a variety of different functional groups. The ring closure was highly stereoselective, leading to the formation of cis-fused systems. Cyclic voltammetry and probe molecules were used to gain mechanistic insight into the reaction. These studies suggested that the key ring closure involved an initial oxidation of the silyl enol ether to a radical cation followed by a furan-terminated cyclization.

Journal ArticleDOI
TL;DR: St stereochemical correlation between the (R) axial chirality of the diketone and the (M) helical chirability of the [7]helicene is established and one such enantiopure trimethylsilyl-substituted [7], which possesses enchanced chiroptical properties and forms a chiral molecular glass.
Abstract: Synthesis of thiophene-based [7]helicenes, which are functionalized for both design of organic chiral glasses with strong chiroptical properties and for further homologation to higher [n]helicenes, is reported The key synthetic transformations are kinetic resolution of the intermediate diketone and the annelation step forming the center benzene ring by means of an intramolecular McMurry reaction Based upon X-ray crystallographic determinations of the absolute configurations for (+)-enantiomers of the diketone and the [7]helicene, stereochemical correlation between the (R) axial chirality of the diketone and the (M) helical chirality of the [7]helicene is established One such enantiopure trimethylsilyl-substituted [7]helicene possesses enchanced chiroptical properties and forms a chiral molecular glass

Journal ArticleDOI
TL;DR: A novel approach to the hydroisobenzofuran core utilizing a TiCl4-mediated [4+3] annulation is reported, and a short synthesis of deacetoxyalcyonin acetate, a member of the eunicellin family, has been achieved.
Abstract: A novel approach to the hydroisobenzofuran core utilizing a TiCl4-mediated [4+3] annulation is reported. This [4+3] annulation protocol provides a short, general route to the hydroisobenzofuran core present in the eunicellin diterpenes. Using this annulation, a short synthesis (17 steps) of deacetoxyalcyonin acetate, a member of the eunicellin family, has been achieved.


Journal ArticleDOI
TL;DR: The four-component coupling-amination-aza-annulation-Pictet-Spengler (CAAPS) sequence of acid chlorides 1, terminal alkynes 2, tryptamine derivatives 6, and acryloyl chloride derivatives 4 represents a facile and rapid one-pot access to tetrahydro-beta-carbolines 7 in moderate to good yields.

Journal ArticleDOI
TL;DR: The use of P(t-Bu)3 as a ligand on palladium was found to be crucial in this annulation reaction, resulting in the exclusive formation of 3-fluoroalkylated benzofurans in high yields.

Journal ArticleDOI
TL;DR: The palladium-catalyzed annulation reaction of a variety of fluorine-containing internal alkynes with 2-iodoaniline derivatives took place smoothly to give the corresponding 2,3disubstituted indol... as mentioned in this paper.
Abstract: The palladium-catalyzed annulation reaction of a variety of fluorine-containing internal alkynes with 2-iodoaniline derivatives took place smoothly to give the corresponding 2,3-disubstituted indol...

Journal ArticleDOI
TL;DR: In this paper, various 6-substituted 5methoxy-δ-lactams were synthesized from α-sulfonyl acetamide in 4 steps in good yield.

Journal ArticleDOI
TL;DR: A new method for the synthesis of unsymmetrical calixarenes is described which involves the reaction of a diyne with a bis-carbene complex of chromium and the proper choice of arene substitution in the starting diyne and the starting carbene complex is presented.
Abstract: A new method for the synthesis of unsymmetrical calix[4]arenes is described which involves the reaction of a diyne with a bis-carbene complex of chromium. This synthesis of calixarenes is unique in that it involves the formation of two of the four benzene rings of the calixarene and the macrocyclic ring of the calixarene in the same step. Thus, two of the four benzene rings of the calixarene are identical, but the other two rings may each be different, giving a general method for the synthesis of calixarenes in which there are either two or three differently substituted benzene rings. This protocol gives access to a large family of unsymmetrical calixarenes by the proper choice of arene substitution in the starting diyne and the starting carbene complex. Nine examples are presented in which the yields in the key triple annulation step range from 22 to 41%. The overall yields of calixarenes from commercially available starting materials compare favorably with those from existing methods for the synthesis o...

Journal ArticleDOI
TL;DR: Aza-Wittig reaction of iminophosphorane 5 with CS2 or CO2 gives the 1,2,4-triazolo[5,1-b]quinazolin-9(3H)-one.

Journal ArticleDOI
TL;DR: In this paper, a one-pot synthesis of the hitherto unreported pyrido[5″,6″:4,5;3,2-d :3′,2′-d ′]dipyrimidine-4,8(3 H, 9 H )-dione 6a- o and pyrazino, based on the tandem aza-Wittig heterocumulene-mediated annulation strategy is described.

Journal ArticleDOI
Karl Gademann1, Yann Bethuel1
TL;DR: The first total synthesis of anachelin H is reported, which was found to be identical to a sample of the natural product, thus confirming the configuration by total synthesis.

Journal ArticleDOI
TL;DR: Experiments with a model substrate indicate that it is likely that a catechol oxidase-type enzyme is involved in the biosynthesis of the anachelin chromophore.
Abstract: A postulated biogenesis forms the basis for a synthetic route to the natural product anachelin H. Key steps include a tellurium-mediated, oxidative aza annulation and a Claisen condensation under mild conditions. Experiments with a model substrate indicate that it is likely that a catechol oxidase-type enzyme is involved in the biosynthesis of the anachelin chromophore.

Journal ArticleDOI
01 Feb 2004-Synlett
TL;DR: The first total synthesis of the furo[3,2-a] carbazole alkaloid furoclausine-A was described in this paper using an iron-mediated construction of the carbazoles framework and an acid-catalyzed annulation of the furan ring as key steps.
Abstract: The first total synthesis of the furo[3,2-a]carbazole alkaloid furoclausine-A is described using an iron-mediated construction of the carbazole framework and an acid-catalyzed annulation of the furan ring as key steps.

Journal ArticleDOI
TL;DR: A multistep one-pot electrochemical synthesis of a variety of complex 2-alkylamino-1,4-benzoxazine derivatives is described, which should be useful to generate libraries of heterocycles.
Abstract: A multistep one-pot electrochemical synthesis of a variety of complex 2-alkylamino-1,4-benzoxazine derivatives is described. The reactions are regiospecific and diastereospecific in the case of heterocyclic annulation. This cascade sequence, wherein both cycloaddition partners are generated in situ, at room temperature, under metal-free conditions, allows the inverse-electron-demand Diels-Alder reaction of an o-iminoquinone diene and a secondary alkylenamine dienophile, two chemically nonaccessible unstable entities. To increase the molecular diversity, a variant in which the enamine is separately prepared completes the aforementioned procedure. The extension of this reaction should be useful to generate libraries of heterocycles.

Journal ArticleDOI
TL;DR: Samarium diiodide promotes smooth reductive cyclizations of gamma-naphthyl-substituted ketones to afford tri- and tetracyclic compounds in high yields and with excellent stereoselectivities.

Journal ArticleDOI
TL;DR: An efficient regiocontrolled synthesis of highly substituted and annulated indazoles involving base induced addition-elimination of 1,3-diphenyl-5-cyanomethylpyrazole to a variety of acyclic and cyclic α-oxoketene, followed by acid assisted cycloaromatization of the resulting conjugate adducts has been reported.

Journal ArticleDOI
31 Dec 2004-Synlett
TL;DR: Fluorescent bicyclic analogs of cytosine have been synthesized directly from derivatives of 5-iodocytosine by a one-pot sequential Sonogashira cross-coupling and annulation with terminal alkynes.
Abstract: Fluorescent bicyclic analogs of cytosine have been synthesized directly from derivatives of 5-iodocytosine by a one-pot sequential Sonogashira cross-coupling and annulation with terminal alkynes. The spectral properties of these compounds depend on the identity of the alkyne. 7-Deazapurines synthesized from substituted phenylacetylenes possess greater fluorescence than those derived from alkyl substituted alkynes.


Journal ArticleDOI
TL;DR: Lewis-base-catalyzed cycloisomerization of bis(enones) to decalins has been demonstrated as an alternative to the traditional Lewis acid catalyzed Diels-Alder cycloaddition.