A solvent-free synthesis of 1,2,3,5-tetrasubstituted pyrroles from enaminones and α-haloketones

A simple synthesis of 1,2,3,5-tetrasubstituted pyrrole derivatives from the reaction of enaminone withα-haloketones,under solvent-free conditions,is described.     

Yb（OTf）3-catalyzed synthesis of pyrroles under solvent-free conditions

A Yb(OTf)_3-catalyzed approach for the synthesis of pyrroles under solvent-free conditions was achieved,which could afford the desired products with yields ranged from moderate to excellent.     

Photoinduced chlorine atom-transfer cyclization/photohydrolysis of 3-acyl-2-chloro-N-(ω-phenylalkynyl)pyrroles: a one-pot synthesis of benzoyl-substituted fused pyrroles

A one-pot synthesis of benzoyl-substituted fused pyrroles or indoles in moderate to high yields has been achieved by the photocyclization/photohydrolysis reactions of N-(ω-phenylalkynyl)-2-chloropyrrole-3-carbaldehydes or 3-acyl-N-(ω-phenylbutynyl)-2-haloindoles in wet acetone. The formation of all these products could be inferred by a two-step reactions, namely, photoinduced chlorine atom-transfer cyclization and subsequent photohydrolysis.     

An EPR analysis of β-dimerization in α-blocked pyrroles in oxidant conditions

Electron paramagnetic resonance (EPR) analysis of neutral and acidic solutions of 2,5-dimethyl-1-phenylpyrrol (1) and meta-, para-, and ortho-bis(2,5-dimethylpyrrol-1-yl)benzenes (4-6) in the presence of Tl(III) trifluoroacetate as oxidant reveals the poor stability of their generated monomeric radical cations which dimerize through C(β)-C(β) bond formation. EPR spectra of the monomeric radical cations 4(?+) , 5(?+) , and 6(?+) coincide with that of 1(?+) , suggesting that the unpaired electron in these charged species is confined in one of the pyrrolic rings. The very twisted angles between pyrrolic and phenyl planes due to steric hindrance in the X-ray analysis of the molecular structure of 4 confirm the absence of extended conjugation in the π-system.     

Three-component synthesis of polysubstituted pyrroles from α-diazoketones, nitroalkenes, and amines

Polysubstituted pyrroles are regiospecifically synthesized via the copper-catalyzed three-component reaction of α-diazoketones, nitroalkenes, and amines under aerobic conditions. The cascade process involves an N-H insertion of carbene, a copper-catalyzed oxidative dehydrogenation of amine, and a [3 + 2] cycloaddition of azomethine ylide.     

Convenient method of preparing 3-substituted 2,2′-furyl(thienyl)pyrroles

2,2-Furyl(thienyl)pyrroles and their 3-decylthio derivatives were synthesized by the Paal-Knorr reaction from the corresponding 3-unsubstituted or 3-decylthio-substituted dimethylacetals of 4-(2-furyl)- and 4-(2-thienyl)-4-oxobutanal. The starting materials were synthesized in three stages from methyl-2-furan- and -2-thiophenecarboxylates. The latter were treated with 1-bromo-2-ethoxycyclopropyllithium via acid-catalyzed methanolysis of the 1-bromo-2-ethoxyketones formed and farther reaction with zinc powder or sodium decylthiolate.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1141–1143, August, 1991.     

Alkylations of Resorcarenes and Calix[4]pyrroles in Phase Transfer Catalytic Systems

Calixlnlarenesarecyclicoligomersmadeupofphenolsandformaldehyde.Thisversatileclassofcompoundshasbeenextensivelystudiedinthelastdecademainlyinordertoobtainnewcomplexingagentsbyappropriatefuntionalizationoftheparentmoleculel.ResorcarenesZandcall-c[4]pyrroles'aretwosubgroupmembersofthefamilyofcalixarensandalsoattractedincreasinginterests.Aspartofaprogrammeaimedatthesynthesisofneweasy-to-makecalixarenemolecules,wedecidedtoinvestigatethealkylationofsomecalixarensinPhaseTransferCatalysis(PTC)condi…     

Expedient synthesis of highly substituted pyrroles via tandem rearrangement of α-diazo oxime ethers

An efficient rhodium-catalyzed synthesis of 2H-azirines and pyrroles has been developed. Novel rearrangement of α-oximino ketenes derived from α-diazo oxime ethers provides 2H-azirines bearing quaternary centers and allows for subsequent rearrangement to highly substituted pyrroles in excellent yields.     

Synthesis of pyrroles through a 4π-electrocyclic ring-closure reaction of 1-azapentadienyl cations

1-Azapenta-1,4-diene-3-ols 4a-m are easily accessible from 1-azapenta-1,4-dien-3-ones 3a-i and organolithium compounds. Treatment of the compounds 4a-m with strong acid (triflic acid) generates 1-azapentadienyl cations in situ upon protonation at the hydroxyl oxygen atom and subsequent water elimination. The intermediate cations undergo facile 4π-electrocyclization under ambient condition to give diversely substituted pyrroles 6a-m in moderate to good yield. The product pyrrole 6k could be characterized by X-ray diffraction. Quantum chemical calculations were performed to elucidate the mechanism of this reaction with respect to starting compounds, transition states, and products. They support the proposed mechanism of a 4π-conrotatory M?bius-type electrocyclic ring-closure reaction.     

Catalyst-free facile and efficient one-pot synthesis of densely functionalized pyrroles and α-amino ketones

An efficient catalyst-free one-pot three-component synthesis of penta-substituted pyrroles has been successfully developed. A variety of penta-substituted pyrroles were straightforwardly synthesized from good to excellent yields (78%–93%) by using easily accessible starting materials under mild conditions. This protocol also provided α-amino ketones in good yields (87%–98%) without column chromatography.     

Synthesis of Calix[4]pyrroles: A Class of New Molecular Receptor

RecentlySesslerandco-workersdiscoveredthatthemeso-octaalkylporphyrinogensshowedinterestinganionandneutralsubstratebindingpropertiesandmightserveasaclassofneweasy-to-makemolecularreceptorintheareaofsupramolecularchemistry'.However,themeso-octaalkylpor...     

Synthesis and crystal structure of 15α,20α-di(4-hydroxylphenyl)calix[4]pyrroles and 10α,20β-di(4-hydroxylphenyl)calix[4]pyrroles

In the presence of methanesulfonic acid as catalyst, the condensation reactions of 5,5′-dialkyldipyrromethanes with p-hydroxyacetophenone in methanol resulted in a mixture of the unexpected polysubstituted 15α,20α-di(4-hydroxylphenyl)calix[4]pyrroles and the expected 10α,20β-di(4-hydroxylphenyl)calix[4]pyrroles in comparable lower yields. The crystal structures of the new calix[4]pyrroles and their oxyacetate derivatives were successfully determined by X-ray diffraction and the intermolecular interactions in the solid state is briefly discussed.     

Enantioselective synthesis of tertiary alcohols through a zirconium-catalyzed Friedel-Crafts alkylation of pyrroles with α-ketoesters

Chiral complexes of 1,1'-bi-2-naphthol-based ligands with zirconium tert-butoxide catalyze the Friedel-Crafts alkylation of pyrroles with α-ketoesters to afford tertiary alcohols in good yields and ee up to 98%. The reaction is also of application to 4,7-dihydroindole to give C2-alkylated indoles after oxidation with p-benzoquinone.     

Chromeno[2,3-c]pyrroles by one-pot multicomponent domino addition–amination reaction

A new aspect concerning chromone chemistry leading to the one-pot synthesis of chromeno[2,3-c]pyrroles is described. The synthesis involves a multicomponent reaction of 3-formylchromones with isocyanides and azodicarboxylates, whereupon novel chromeno[2,3-c]pyrrole derivatives were formed in good yields. The structures of the products were elucidated by 1D and 2D NMR experiments and were unambiguously confirmed by the use of crystal X-ray diffraction analysis. Full assignment of all ¹H and ¹³C NMR chemical shifts has been achieved. A plausible mechanistic scheme is proposed.     

Scope and Applicability of an Expedient Synthesis Leading to Polysubstituted 3‐(Carboxyphenyl)pyrroles

A convenient three‐step route toward a functionalized pyrrole building block for novel anti‐inflammatory agents is reported. In contrast to previous strategies, the present approach focuses on inexpensive starting materials and application on a multigram scale. A high degree of functional diversity is demonstrated in various derivatives, and the scope and limitations of this route are discussed. Complementary to the described tetrasubstituted pyrroles, a novel ring‐closure protocol based on the Feist–Benary condensation affords trisubstituted analogues.     

Synthesis of β-octabromocalix[4]pyrroles and conformational diversity in their acetone inclusion complexes

Two β-octabromocalix[4]pyrroles were synthesized using a modified strategy, which provides the advantage of large scale preparation with rapid purification. The acetone inclusion complexes of these compounds show different structural orientations featuring diverse types of novel hydrogen bonding owing to varied meso-substitution along with the presence of eight peripheral bromine atoms.     

1,2- and 1,2,5-substituted pyrroles from an (η5-pyrroly)-transition metal complex

Reaction of (L)(Ph₃P)₂ReH₂ (L = η⁵-pyrroly) with acyl chlorides leads directly to N-acylpyrroles in high yields; with methyl triflate cations (L′)(Ph₃P)₂ReH₂⁺ (L = η⁵-N-methylpyrrole) are formed, which release N-methylpyrroles by heating in DMSO.     

An approach to the Paal–Knorr pyrroles synthesis in the presence of β-cyclodextrin in aqueous media

An efficient and facile method for the synthesis of N-substituted pyrroles in moderate to good yields by the Paal–Knorr reaction of γ-diketones with amines in the presence of β-cyclodextrin in aqueous media has been developed.Moreover,this process tolerated diamines(e.g.,para-,meta- or orthophenylenediamine)to construct bis-pyrrole or mono-pyrrole derivates.β-Cyclodextrin can be recovered easily after the reactions and reused without evident loss in activity.