EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2010
Chintakunta Ramesh
Abstract An unprecedented route for the synthesis of 3,3,-biindoles is developed. Both symmetrical and unsymmetrical 3,3,-biindoles could be generated by this method. Mild conditions, high yields of the products, and environmentally acceptable reagent are the merits of the procedure. [source]

Broadening the Synthetic Scope of the Iron(III)-Catalyzed Aza-Prins Cyclization

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2010
Rubén M. Carballo
Abstract The nature and influence of the N -sulfonyl group in aza-Prins cyclization and the reactivity of the six-membered aza-cycle generated has been studied. The aza-Prins cyclization of ,,,-unsaturated amines with a tosyl group at the nitrogen atom produces 2-alkyl-4-halo-1-tosyl-1,2,5,6-tetrahydropyridines with a halovinyl function, extraordinarily stable to further derivatization and detosylation conditions. To modulate the reactivity of such aza-cycles, a general study of the aza-Prins cyclization reaction was performed with several sulfonamides. Ring formation occurs satisfactorily with both N -nosyl and N -mesylamines providing optimal conditions for further synthetic transformations. To exemplify the scope of this methodology, a short synthesis of the alkaloid coniine was successfully carried out. [source]

Unexpected Synthesis of Rearranged 3,4-Dihydroquinazolines by a Sequential Ugi 4CC/Aza-Wittig/Carbodiimide-Mediated Cyclization

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2010
Ping He
Abstract The 2,3,4-trisubstituted 3,4-dihydroquinazolines 4 were unexpectedly obtained from a sequential Ugi four component condensation (4CC)/aza-Wittig/carbodiimide-mediated cyclization. [source]

CuI -Catalyzed Azide,Alkyne Intramolecular i -to-(i+4) Side-Chain-to-Side-Chain Cyclization Promotes the Formation of Helix-Like Secondary Structures

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2010
Mario Scrima
Abstract A solid-phase assembly of model peptides derived from human parathyroid hormone-related protein (11,19) containing ,-azido- and ,-yl-,-amino acid residues in positions i and i+4 was cyclised in solution by an intramolecular CuI -catalyzed azide,alkyne 1,3-dipolar Huisgen cycloaddition. These series of heterodetic cyclo-nonapeptides varied in the size of the disubstituted 1,2,3-triazolyl-containing bridge, the location and the orientation of the 1,2,3-triazolyl moiety within the bridge. The 1,2,3-triazolyl moiety, presented at either 1,4- or 4,1-orientation, is flanked by side chains containing 1,4 CH2 groups that result in bridges comprised from 4,7 CH2 groups connecting residues 13 and 17. Comprehensive conformational analysis employing CD, NMR and molecular dynamics reveals the conformational propensities of these heterodetic cyclo-nonapeptides. Cyclo-nonapeptides containing either the 7 methylene bridge (VII and VIII) or the 4 methylene bridge (II) are unstructured in structure-promoting solvent. Cyclo-nonapeptide I in which the 1,4-disubstituted 1,2,3-triazolyl is flanked by 3 and 1 CH2 groups in proximity to the respective residues 13 and 17, is stabilized in a non-canonical structure. All the other heterodetic cyclo-nonapeptides (III,VI) in which the 1,2,3-triazolyl is flanked by a total of 5 or 6 CH2 groups nicely accommodate ,-helical structures and reproduce very closely the helical structure stabilized by the analogous cyclo-nonapeptide in which Lys13 and Asp17 are bridged by the isosteric lactam. These studies suggest that the bioorthogonal i -to-(i+4) side-chain-to-side-chain cyclization via the prototypic "click reaction" offers a new and powerful approach for generating stable helix mimetic structures. [source]

Cyclization of Trichloroacetimidates by Olefin Aminopalladation ,-Heteroatom Elimination

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 36 2009
Ansis Maleckis
Abstract The cyclization of ,-acetoxy- O -allyl- and ,-acetoxy- O -homoallyl-trichloroacetimidates to 4-vinyloxazolines and a 4-vinyldihydrooxazine has been efficiently achieved by olefin aminopalladation,,-heteroatom elimination. (Z)-Allylic imidates bearing a secondary ,-acetoxy group underwent PdII -catalysed cyclization to give the E isomers of 4-vinyloxazolines selectively and gave no Overman rearrangement products. Using a chiral substrate, it has been demonstrated that cyclization to 4-vinyloxazolines occurs with high chirality transfer. Stereoselective E isomer formation and chirality transfer provided a basis from which to discuss the possible reaction mechanism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Efficient and Selective Method for the Synthesis of Dihydrodipyridopyrazines Based on the Pd-Catalysed Amination of Halopyridines

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2009
Oana-Irina Patriciu
Abstract A novel methodology for the efficient and selective synthesis of isomers A and B of N -substituted dihydrodipyridopyrazines was developed. The key step is the intermolecular coupling of aminopyridines and halonitropyridines/dihalopyridines in the presence of a catalyst system composed of Pd(OAc)2/Xantphos. This system displays good functional group compatibility and the desired C,N bond-forming process proceeds in good yields. Cyclization of suitable nitro-substituted N,N, -dipyridinylamines produces monosubstituted dihydrodipyridopyrazines, which can easily be alkylated to give a large variety of unsymmetrical 5,10-dialkyl-5,10-dihydrodipyrido[2,3- b:2,,3,- e]pyrazines (isomers A) and 5,10-dialkyl-5,10-dihydrodipyrido[2,3- b:3,,2,- e]pyrazines (isomers B). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Synthesis of Polysubstituted 3-Iodopyrans by Electrophilic Cyclization

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2009
Yong-Xin Xie
Abstract A variety of polysubstituted 3-iodopyrans were readily prepared in good to excellent yield under mild reaction conditions by the reaction of alkynyl carboxamides with ICl, I2, and NIS. The products obtained from this process are versatile materials that can be used to construct other complex functionalized pyran structures of importance. The occurrence of the pyranyl group in both natural products and pharmaceuticals confers important value to this study. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Application of 7- endo - trig Pictet,Spengler Cyclization to the Formation of the Benzazepine Ring: Synthesis of Benzazepinoindoles,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2009
Sudhir K. Sharma
Abstract The preparation of benzazepinoindoles, fused heterocycles with a benzazepine moiety, was accomplished through an intramolecular 7- endo - trig Pictet,Spengler cyclization. The precursors comprising C-3- or C-2-linked o -aminobenzylindoles required for the cyclization were obtained either by treating indoles with o -nitrobenzyl bromide followed by reduction of the nitro group or by treating 2-nitrophenylacetic acid with DCC/DMAP followed by reduction of the aryl nitro functionality. Resulting substrates 5 and 6 were then subjected to the 7- endo - trig Pictet,Spengler reaction with a variety of aldehydes and ketones to furnish new polycyclic structures benzazepinoindoles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Straightforward Strategy for the Stereoselective Synthesis of Spiro-Fused (C-5)Isoxazolino- or (C-3)Pyrazolino-(C-3)quinolin-2-ones from Baylis,Hillman Adducts by 1,3-Dipolar Cycloaddition and Reductive Cyclization,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 32 2008
Virender Singh
Abstract A straightforward and general approach for the stereoselective synthesis of spiro-fused (C-5)isoxazolino- or (C-3)pyrazolino-(C-3)quinolin-2-ones from the adducts offorded from the Baylis,Hillman reaction of 2-nitrobenzaldehyde and ethyl acrylate by sequential 1,3-dipolar cycloaddition and reductive cyclization is presented. It was found that the reductive cyclization of the isoxazoline derivatives proceeded efficiently in the presence of In/HCl, whereas similar reductions of pyrazolines gave better yields when carried out in the presence of an Fe/AcOH mixture. However, similar attempts employing the Baylis,Hillman adduct of 2-nitrobenzaldehyde and methyl vinyl ketone did not yield the desired compounds.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Synthesis of Novel Angular Heterocyclic Lignans by an InCl3 -Catalyzed Friedel,Crafts-Type Cyclization

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2008
Matthieu Dorbec
Abstract The synthesis of a 1-aryltetralin privileged structure-based library of novel angular heterocyclic lignans is described. Indolotetralins 3, tetrahydroquinolinotetralins 4, and thiochromanotetralins 5 were obtained from the methyl ester of thuriferic acid 2 according to a three-step procedure involving an InCl3 -catalyzed Friedel,Crafts-type cyclization as the key step.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Synthesis of Tyrosine-Derived Tetrahydroisoquinolines by Lewis Acid Catalyzed Cyclization of N -(Phenylsulfonyl)alkyloxazolidinones,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2007
Stefan Tussetschläger
Abstract N -Boc-protected tyrosine esters 5a,b were converted into tetrahydroisoquinolines 13 and 14 in four steps by reduction and ring closure to oxazolidinones 9 and 10, addition of benzenesulfinic acid and aldehydes to sulfones 11 and 12 and subsequent Lewis acid catalyzed cyclization. In the case of m -tyrosine derivative 5a, selective protection with bromine prevented the formation of undesired regioisomers. Debromination of target compounds 13 was readily achieved under radical reduction conditions by using Bu3SnH/AIBN. Tetrahydroisoquinolines 13 and 14 were isolated as single diastereomers whose trans configuration was confirmed by X-ray crystal structure analysis. Partial epimerization of trans - 13i and trans - 21 to the corresponding cis diastereomers was achieved under basic conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Stereoselective Synthesis of 2-Deoxyglycosides from Sulfanyl Alkenes by Consecutive "One Pot" Cyclization and Glycosylation Reactions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2007
Miguel A. Rodríguez
Abstract 2-Deoxy-2-iodopyranosides 3, and 9,12 were synthesized from sulfanyl alkenes using a "one pot" consecutive cyclization,glycosylation process. Compared with the stepwise procedure, the "one pot" process gave significantly improved yields with similar or slightly lower selectivities. The "onepot" procedure was applied to the synthesis of 2,6-dideoxy-2-iodoglycoside 22, which was successfully deiodinated to afford the 2,6-dideoxyglycoside 23. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Concise Synthesis of 2,6-Disubstituted Morpholines by Cyclization of Epoxy Alcohols

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2007
Domenico Albanese
Abstract A novel, straightforward and high yielding synthesis of enantiomerically pure 2,6-disubstituted morpholines was developed by acid-catalyzed cyclization of epoxy alcohols. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Synthesis of Benzomorphan Analogues by Intramolecular Buchwald,Hartwig Cyclization

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2007
Anton S. Khartulyari
Abstract A new strategy toward the important class of benzomorphans is described. The key bond formation is based on an intramolecular Buchwald,Hartwig enolate arylation reaction. Thus, alkylation of piperidones with ortho -bromobenzyl bromides provides the necessary substrates. In the presence of a palladium catalyst, a sterically hindered phosphane ligand, and a base, carbon,carbon bond formation to tricyclic benzomorphan derivatives takes place. After removal of the N -protecting group, derivatization reactions are possible. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Ruthenium(II)-Catalyzed Cyclization of Oxabenzonorbornenes with Propargylic Alcohols: Formation of Isochromenes

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2006
Karine Villeneuve
Abstract The ruthenium-catalyzed cyclization of a propargylic alcohol with an oxabenzonorbornene in methanol leads to an unanticipated isochromene framework. The catalytic cycle to form this product is believed to go through an oxidative cyclization of the two unsaturated partners with the ruthenium catalyst, followed by ,-hydride elimination, tautomerization andhydroruthenation. The ruthenacyclobutane thus obtained further undergoes [2+2] cycloreversion to form a ruthenium,carbene intermediate that atypically rearranges via a [1,3]-alkoxide shift and finally reductively eliminates to produce the desired compound. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Stereoselective Disposition of the Geminal Dimethyl Group in the Cyclization of Geranyl Acetate under Zeolite Confinement Conditions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006
Constantinos Tsangarakis
Abstract The stereochemistry in the acid-catalysed biomimetic cyclization of [8,8,8-D3]geranyl acetate was examined in solution and under conditions of zeolite Y confinement. In the intrazeolite reaction the gem -allylic methyl group adopts a diastereoselective disposition in the cyclization product (64,% dr). In contrast, the gem -dimethyl disposition in a homogeneous medium (ClSO3H/2-nitropropane) proceeds with negligible diastereoselectivity (dr < 5,%). The enhanced diastereoselection within the zeolite is attributed to the proximity of the nucleophilic double bond to the intermediate carbocation, as a result of confinement (entropy effect). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Synthesis of Enantiomerically Pure 2,3,4,6-Tetrasubstituted Tetrahydropyrans by Prins-Type Cyclization of Methyl Ricinoleate and Aldehydes,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2006
Ursula Biermann
Abstract The AlCl3 -catalyzed Prins-type cyclization of methyl ricinoleate (1), an enantiomerically pure renewable compound, with aldehydes such as heptanal (2a), isobutyraldehyde (2b), pivaldehyde (2c) and benzaldehyde (2d) is a simple reaction for the diastereoselective synthesis of enantiomerically pure 2,3,6-trialkyl-substituted 4-chlorotetrahydropyrans. The respective 4-hydroxytetrahydropyrans are obtained e.g. with aldehydes 2a and 2d using montmorillonite KSF/O as the catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Double Cyclization of Bis(,-hetarylmethyl)amino Esters to Optically Active Bridged N-Heterocycles of HIV-Inhibiting Activity

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2004
Heike Faltz
Abstract Anellated 1-azabicyclo[3.3.1]nonanes 6 were synthesized by several routes starting from natural ,-amino esters 2 and o -haloaryl- or o -bromohetarylmethyl bromides 1. N -Alkylation of the starting amino esters to 5 and 3 was followed by halogen/lithium exchange and double cyclization. The cyclization products 6 exhibit interesting inhibition of RNase H and DNA-polymerase activity of reverse transcriptase (RT) of HIV-1 at concentrations where human cellular DNA polymerases are not affected. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

A Mechanistic Rationale for the Mode Selectivity in the Intramolecular Cyclization of Ethylene-Tethered Iminoketenimines: [2+2] versus [4+2] Stepwise Cycloadditions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2004
Mateo Alajarín
Abstract A stepwise mechanism, via a zwitterionic intermediate, has been established by ab initio and DFT calculations for the intramolecular cyclization of N -(3-azabut-3-enyl)ketenimine into its corresponding [2+2] cycloadduct. The control of the mode selectivity ([2+2] versus [4+2] cycloaddition) in the intramolecular cyclization of C -vinyl- N -(iminoethylene)ketenimines, which favors the [4+2] cycloadducts, also has been rationalized by comparing the energies calculated for both reaction pathways; the results have been confirmed by a quantitative kinetic analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

The Stereoselective Total Synthesis of (6S)-5,6-Dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H -pyran-2-one via Prins Cyclization

HELVETICA CHIMICA ACTA, Issue 7 2010
Jhillu, Singh Yadav
Abstract The stereoselective total synthesis of an antiproliferative and antifungal , -pyrone natural product (6S)-5,6-dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H -pyran-2-one is described. The key steps involved are the Prins cyclization, Mitsunobu reaction, and ring-closing metathesis reaction. [source]

Synthesis of 3-Acyl-4-alkenylpyrrolidines by Platinum-Catalyzed Hydrative Cyclization of Allenynes

HELVETICA CHIMICA ACTA, Issue 8 2006
Takanori Matsuda
Abstract A series of nitrogen-tethered allenynes (,5-aza-1,2-dien-7-ynes') 1 were transformed to the corresponding 3-acyl-4-alkenylpyrrolidines 3 when treated with a catalytic amount of PtCl2 in MeOH at 70°. Initial Pt-promoted cyclization forms a nonclassical carbocationic intermediate. In contrast to the cycloisomerization in toluene, which produced the bicyclic cyclobutenes 2, the intermediate is intercepted by addition of an oxygen nucleophile to achieve the formal hydrative cyclization. [source]

On the Scope of a Prins -Type Cyclization of Oxonium Ions

HELVETICA CHIMICA ACTA, Issue 11 2004
Georg Fráter
The Prins cyclization of an aldehyde 1 with a homoallylic alcohol 2, affording tetrahydro-2H -pyrans 4via the oxonium ion 3 as central intermediate, was conceptually transferred to (alk-3-enyloxy)acrylates 6, which form a related oxonium ion 7 upon treatment with acids (Scheme,1). The scope and utility of this modification of the Prins -type cyclization of oxonium ions is discussed exemplarily by means of the syntheses of ten tetrahydro-2H -pyran and tetrahydrofuran derivatives, featuring diverse substitution patterns as well as different degrees of molecular complexity. These target structures include (±)-ethyl (2RS)-2-[(2RS,4SR,6RS)- and (2SR,4RS,6SR)-2-tetahydro-4-hydroxy-6-methylpyran-2-yl]propanoate (23), (±)-ethyl [(2RS, 3RS)-tetrahydro-3-isopropenylfuran-2-yl]acetate (32), (±)-ethyl (2Z)-3-(tetrahydro-2,2-dimethylfuran-3-yl)acrylate (37), (±)-(3aRS,6RS, 7aRS)-octahydro-7a-methylbenzofuran-6-yl formate (42), (±)-ethyl (2RS,3RS,4aRS,8SR,8aRS)-hexahydro-2,5,5,8-tetramethyl-7-oxo-2H,5H -pyrano[4,3- b]pyran-3-carboxylate (48), and (±)-ethyl (2RS,3RS,6SR)-tetrahydro-6-(2-methoxy-2-oxoethyl)-3-methyl-2H -pyran-2-carboxylate (53) (see Schemes,3 and 5,8). Besides the stereochemistry and mechanistic details of this versatile oxonium-ion cyclization, the synthesis of suitable starting materials is also described. [source]

Heterocyclic synthesis containing bridgehead nitrogen atom: Synthesis of 3-[(2H)-2-oxobenzo[b]pyran-3-yl]- s -triazolo[3,4- b]-1,3,4-thiadiazine and thiazole derivatives

HETEROATOM CHEMISTRY, Issue 2 2003
M. A. Raslan
The reaction of 2H-2-oxobenzo[b]pyran-3-hydrazide (2) with carbon disulfide in basic DMF afforded potassium thiocarbamate 3, which readily underwent heterocyclization upon its reaction with hydrazine and/or phenacyl bromide to yield 1,2,4-tiazole (4) and thiazole 7 derivatives, respectively. Condensation of 4 with substituted phenacyl bromide and/or chloranil gave 1,2,4-triazole[3,4-b]thiadiazine (5a,b) and 3,10-bis-[2H-2-oxobenzo[b]pyran-3-yl]-6,13-dichloro-bis-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazino[5,,6,-b:5,,6,-e]cyclohexa-1,4-diene (6), respectively. Cyclization of thiosemicarbazide 10 by refluxing it in sodium hydroxide and/or phosphoryl chloride afforded triazole 13 and thiadiazole 15 derivatives, respectively. Also, 10 reacted with phenacyl bromide in the presence of anhydrous sodium acetate to give the oxothiazolidine derivative 17. The structure of the synthesized compounds were confirmed by elemental analyses, IR, 1H NMR, and mass spectra. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:114,120, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10109 [source]

Sulfur-Assisted and 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)-Catalyzed Cyclization of 2-Alkynylanilines for the Metal-Free Synthesis of Indole Derivatives

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010
Hongwei Zhou
Abstract A sulfur-assisted and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-catalyzed cyclization of 2-alkynylanilines for the metal-free synthesis of indole derivatives is reported. As a result of the metal-free process, the ready availability of the starting materials and the simple and convenient operation, the type of reaction presented here has potential utility in organic synthesis. A 10-gram scale preparation may demonstrate the possibility of its application in the environmentally friendly synthesis of indole derivatives. [source]

Efficient Synthesis of 2-Fluoromethylated Quinolines via Copper-Catalyzed Alkynylation and Cyclization of Fluorinated Imidoyl Iodides

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010
Shan Li
Abstract 2-Fluoromethylated quinolines were synthesized through the reaction of N -aryl-fluorinated imidoyl iodides with terminal alkynes in good yields by the catalysis of copper(I) iodide (CuI) alone. [source]

Ring Expansion versus Cyclization in 4-Oxoazetidine-2- carbaldehydes Catalyzed by Molecular Iodine: Experimental and Theoretical Study in Concert

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010
Benito Alcaide
Abstract Molecular iodine (10,mol%) efficiently catalyzes the ring expansion of 4-oxoazetidine-2-carbaldehydes in the presence of tert -butyldimethylsilyl cyanide, or allylic and propargylic trimethylsilanes to afford protected 5-functionalized-3,4-dihydroxypyrrolidin-2-ones with good yield and high diastereoselectivity, through a C3C4 bond cleavage of the ,-lactam nucleus. Interestingly, in contrast to the iodine-catalyzed reactions of 3-alkoxy-,-lactam aldehydes which lead to the corresponding ,-lactam derivatives (rearrangement adducts), the reactions of 3-aryloxy-,-lactam aldehydes under similar conditions gave ,-lactam-fused chromanes (cyclization adducts) as the sole products, through exclusive electrophilic aromatic substitution involving the C3 aromatic ring and the carbaldehyde. In order to support the mechanistic proposals, theoretical studies have been performed. [source]

Base- and Copper-Catalyzed Intramolecular Cyclization for the Direct Synthesis of Dihydrofurans

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010
Yong-Fei Chen
Abstract A simple and convenient synthetic approach to dihydrofurans has been developed from the cyclization of 2-propynyl-1,3-dicarbonyl compounds catalyzed by potassium tert -butoxide, copper(II) trifluoromethanesulfonate and triphenylphosphine using methanol/dichloromethane as the solvent under very mild conditions. Moreover, dihydrofurans could be easily transformed into the corresponding furans in the presence of trifluoroacetic acid. [source]

One-Pot Three-Step Synthesis of Naphtho[2,3- a]carbazole- 5,13-diones using a Tandem Radical Alkylation,Cyclization, Aromatization Reaction Sequence

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010
Chunyong Ding
Abstract A three-step, one-pot tandem reaction including radical nucleophilic alkylation/cyclization/aromatization was developed using 0.3 equivalents of silver(I) acetate (AgOAc) as the catalyst and 2 equivalents of ammonium persulfate [(NH4)2S2O8] as the oxidant. This strategy is highly efficient for the assembly of pentacyclic complex carbazoles from aryl-fused bromobenzoquinones and indol-3-ylpropanoic acid acids in 52,72% overall yields (three steps). This new approach provides a significant improvement over the previously reported methods and would greatly facilitate analog library construction of pentacyclic complex carbazoles and benefit further biological evaluation of these compounds. [source]

Copper(II) Bromide/Boron Trifluoride Etherate-Cocatalyzed Cyclization of Ketene Dithioacetals and p -Quinones: a Mild and General Approach to Polyfunctionalized Benzofurans

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010
Yingjie Liu
Abstract A new application of copper(II) bromide-activated ketene dithioacetals as nucleophiles in organic chemistry has been developed. Under the cocatalysis of copper(II) bromide (2.0,mol%) and boron trifluoride etherate (10,mol%), the conjugate addition and sequential cyclization of ,-electron-withdrawing group-substituted ketene dithioacetals with p -quinones in acetonitrile at room temperature gave a variety of benzofurans. This formal [3+2],cycloaddition provides a general method for catalytic synthesis of polyfunctionalized benzofurans with the advantages of readily available starting materials, cheap catalysts, mild reaction conditions, good yields and wide range of synthetic potential for the benzofuran products. Further transformations of the resulting benzofurans to 2-aminobenzofurans and benzofuro[2,3- d]pyrimidine derivatives are also investigated. [source]

Phase-Transfer-Catalyzed Intramolecular Cyclization of ortho -Alkynyl Phenyl Ether Derivatives for Synthesis of 2,3-Disubstituted Benzo[b]furans

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010
Jie Hu
Abstract A variety of substituted benzo[b]furans are readily prepared in good to excellent yields under the mild reaction conditions from o -(1-alkynylphenoxy)-1-phenylethanone under phase-transfer catalysis (PTC). This methodology accommodates simple experimental operations, inexpensive and environmentally benign catalysts, metal catalyst-free conditions, facile reagents and the possibility to conduct large-scale preparations. The development of carbon-carbon bond formation processes via an overall structural isomerization represents the most atom-economical approach. [source]