Color-Tunable Indolizine-Based Fluorophores and Fluorescent pH Sensor

A new fluorescent indolizine-based scaffold was developed using a straightforward synthetic scheme starting from a pyrrole ring. In this fluorescent system, an N,N-dimethylamino group in the aryl ring at the C-3 position of indolizine acted as an electron donor and played a crucial role in inducing a red shift in the emission wavelength based on the ICT process. Moreover, various electron-withdrawing groups, such as acetyl and aldehyde, were introduced at the C-7 position of indolizine, to tune and promote the red shift of the emission wavelength, resulting in a color range from blue to orange (462–580 nm). Furthermore, the ICT effect in indolizine fluorophores allowed the design and development of new fluorescent pH sensors of great potential in the field of fluorescence bioimaging and sensors.     

B(C6F5)3-Catalyzed Aza-Friedel–Crafts Reaction of Indolizines with 2-Aryl-3H-indol-3-ones

A Friedel–Crafts reaction of indolizines with 2-aryl-3H-indol-3-ones catalyzed by B(C₆F₅)₃ is described. This protocol gives access to indolizine derivatives that are valuable building blocks in synthetic and pharmaceutical chemistry. The reaction proceeds under mild conditions, affording various C2-quaternary indolin-3-ones based on indolizine with high yields and regioselectivities. Moreover, the synthetic transformations of the target products were realized by N-methylation and trifluoromethane sulfonation.     

Electrochemical studies of biologically active indolizines

The electrochemical behavior of indolizine ethers, esters, tosylates, sulfonates and other indolizine and azaindolizine derivatives has been investigated by cyclic voltammetry and preparative electrolysis. The cyclic voltammetric data show that the E° values, taken as the midpoints between the anodic and cathodic peak potentials, are sensitive to the identities of the substituents at C-1, C-2 and C-7 positions. The E° values have been correlated with the Hammett substituent parameters. As expected, low E° values are seen for electron donating substituents and higher E° values are seen for electron withdrawing substituents. The cyclic voltammograms of indolizine derivatives with an oxygen atom connected to the C-1 position exhibit a one-electron reversible oxidation and a further, less well-defined, one-electron irreversible oxidation at higher E° values. The cyclic voltammograms of indolizines with hydrogen atom or thienyl substituents connected to the C-1 position exhibit only a one-electron irreversible oxidation. Electrochemical bulk oxidations of indolizines with an oxygen atom at the C-1 position afforded oxoindolizinium salts in decent yields, whereas indolizines with a hydrogen atom at C-1 afforded 1,1′ dimers of indolizines as products in good yields. Bulk oxidation of 1-(α-hydroxybenzyl)-2,3-diphenylindolizine-7-carbonitrile afforded an unexpected ketone product in which the carbonyl group of the indolizine is connected at C-8 instead of at the C-1 position of the starting material. The findings described herein support our hypothesis that certain indolizine derivatives may inhibit lipid peroxidation by an electron transfer mechanism.     

Diastereoselective synthesis of new polyhydroxylated indolizidines from (l)-glutamic acid

A diastereoselective synthesis of two new swainsonine's analogues 1a and 1b with the piperidine ring fused to a phenyl nucleus at C6-C7, namely (1R, 2S, 10R, 10aR)-(+)-1,2,10-trihydroxy-1,2,3,5,10,10a-hexahydrobenzo[f] indolizine (1a) and (1S, 2R, 10R, 10aR)-(+)-1,2,10-trihydroxy-1, 2, 3, 5, 10, 10a-hexahydrobenzo[f] indolizine (1b), is described. Throughout this work, the effectiveness of the tricyclic indolizidine dione 5, readily available in three steps from the cheap l-glutamic acid, as an attractive platform for chemo- and stereodivergent transformations is illustrated. The key steps involved totally diastereoselective ketone reduction of compound 5 and catalytic cis-dihydroxylation of the unsaturated amide 10. The synthetic strategy also allowed for the diastereoselective synthesis of benzoanalogues of the 1,8a-di-epi-lentiginosine 3a ((1R, 2S, 10aR)-(+)-1,2-dihydroxy-1, 2, 3, 5, 10, 10a-hexahydrobenzo[f]indolizine) and 2,8a-di-epi-lentiginosine 3b ((1S, 2R, 10aR)-(+)-1,2-dihydroxy-1,2,3,5,10,10a-hexahydrobenzo[f]indolizine).     

A novel approach to 3-acylated indolizine structures via iodine-mediated hydrative cyclization

We have discovered a new route to 3-acylated indolizine structures via iodine-mediated hydrative cyclization. Reaction mechanism is proposed for this novel transformation, which involves a 5-exo-dig iodocyclization, deprotonation, incorporation of another iodo group, deprotonation, and subsequent replacement of the diiodo group by H₂O. Various 3-acylated indolizine derivatives were obtained using this mild procedure in good yields.     

Photochemical behaviour upon the inclusion for some volatile organic compounds in new fluorescent indolizine β-cyclodextrin sensors

The potentialities of three new fluorescent indolizine modified β-cyclodextrin have been investigated as molecular chemosensors. The pyridin-4-ylindolizine β-cyclodextrin derivatives were synthesised by an amidation between the fluorescent indolizine derivatives and 6-deoxy-6-amino-β-cyclodextrin. The multiconformational search by MM3 and AM1 method in gaseous state and in water respectively suggest the “open cavity” structure as the most probable. These compounds have been characterised spectroscopically by their emission spectra and their sensing ability towards 1-adamantanol, phenol and p-cresol. The fluorescent properties and sensitivity factor of the sensor containing an indolizine product with a perfluored aromatic fragment recommended it fairly as sensor for the detection of volatile organic compounds (VOCs), while the other two sensors, with an aliphatic fragment, can be utilised as biological markers. Finally, a significant bathochromic shift is observed for the sensor containing a t-butyl fragment, in such a way that this sensor may also lead to the detection of VOCs.     

Synthesis of a new fluorinated fluorescent β-cyclodextrin sensor

The synthesis of a new fluorescent sensor incorporating a fluorinated indolizine unit bound to 6-amino-β-cyclodextrin by two different synthetic ways is described. Its sensing ability toward adamantanol has been demonstrated.     

Novel porphyrin-quinone architectures via 1,3-dipolar cycloaddition reactions

Porphyrinic pyridinium ylides react with 1,4-benzoquinone and 1,4-naphthoquinone to afford novel meso-substituted indolizine porphyrins.     

4-甲基吡咯并[2,1,5-cd]中氮茚的合成

以2-乙基吡啶生成的叶立德为原料,采用1,3-偶极环加成反应,得到了一系列3-乙酰基(或苯甲酰基)-5-乙基中氮茚衍生物,后者与KOH在加热条件下发生分子内缩合,得到了一系列4-甲基吡咯并[2,1,5-cd]中氮茚.     

One pot three-component regioselective and diastereoselective synthesis of halogenated pyrido[2,1-b][1,3]oxazines

Three-component reactions of 3-substituted pyridines, dimethyl acetylenedicarboxylate (DMAD), and α-halo ketones led to regioselective and stereoselective synthesis of pyrido[2,1-b][1,3]oxazines in high to excellent yields under mild conditions. All the reactions gave the pyrido[2,1-b][1,3]oxazine derivatives without formation of any indolizine products.     

A one-pot synthesis of substituted pyrido[2,3-b]indolizines

An efficient and novel approach to the synthesis of substituted pyrido[2,3-b]indolizine-10-carbonitriles was developed. These structures are practically unavailable through previously described methods. The cascade transformation involves the reaction of α,β-unsaturated carbonyl compounds with a stable dimer prepared from 1-(cyanomethyl)pyridinium chloride. The reaction was performed under reflux conditions in ethanol/water and in the presence of sodium acetate. This procedure represents a eco-friendly regioselective approach to the pyrido[2,3-b]indolizine core structure.     

Hydrogenation of compounds containing an indolizine moiety and of 1-benzylisoquinoline over rhenium heptasulfide

It was shown by hydrogenation of 2,8-diphenylindolizine, benzo[2,3]indolizine, dibenzo[2,3;5,6]indolizine, dibenzo[ 2,3;7,8 ]indolizine, 1-benzylisoquinoline, and 2,3-dimethyl-6-ethyl-4-(4-nitrophenyl)pyridine over Re₂S₇ (250°C, = 140 atm, 4 h) that the pyridine ring in benzoindolizines is hydrolyzed in preference to the pyrrole ring. Phenyl substituents at the indolizine do not prevent its complete reduction while alkyl substituents make reduction difficult. Annelation of the pyrrole and pyridine rings of indolizine lower the degree of its reduction; a nitro group is reduced to an amino group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1413–1416, June, 1991.     

Potential antitumor agents. III. Synthesis of pyrazolo[3,4-e]pyrrolo[3,4-g]indolizine and 1H-pyrazolo[3,4-e]indolizine derivatives

The preparation of 5-dimethylaminoethyl-4,6-dioxo-1-phenyl-1,4,5,6-tetrahydropyrazolo[3,4-e]pyrrolo-[3,4-g]indolizine, a derivative of the still unknown tetracyclic parent ring pyrazolo[3,4-e]pyrrolo[3,4-g]indolizine, is reported starting from 1-phenyl-5-(1-pyrryl)pyrazole-4-acetonitrile by PPA catalyzed double cyclization of the related oxalylcyanomethyl derivative and subsequent alkylation. The synthesis of 4,5-bis(isopro-pylaminocarbonyloxymethyl) and 4,5-bis-(cyclohexylaminocarbonyloxymethyl) derivatives of 1-phenyl-1H-pyrazolo[3,4-e]indolizine is also described. The new tricyclic and tetracyclic derivatives were tested as potential antitumor agents.     

Valenzisomere aromatischer systeme. Die Synthese des Pyrrolo-3-azabenzvalens

Valence Isomers of Aromatic Systems. The Synthesis of Pyrrolo-3-azabenzvalene 4-Azapentalenyl anion ( 4 ) is shown to react with dichloromethane/butyl lithium in two fundamentally different ways depending on whether diethyl ether or tetrahydrofuran is chosen as solvent. In the first case a tetracyclic valence isomer of indolizine, i.e. pyrrolo-3-azabenzvalene ( 6 ) is formed together with indolizine ( 8 ) itself. In THF however, a pyrrylbutenyne ( 9 ), isomeric with the products mentioned above is obtained in a stereospecific reaction. Once again the appearance of indolizine ( 8 ) accompanies the reaction. Mechanistic implications, based on the finding that the heterovalene 6 is not a precursor of the pyrrylbutenyne 9 , are discussed.     

Synthesis of decahydropyrrolo[2,1,5-cd]indolizine derivatives through RuCl3/AgOTf induced alkene–alkene and alkene–arene double cycloisomerizations

In the presence of RuCl₃/AgOTf, pyrrolizidine derivative with styrenyl substituents at the 3,5-positions undergo a 6-exo-trig cyclization and subsequent intramolecular Friedel–Crafts reactions to form decahydropyrrolo[2,1,5-cd]indolizine or decahydrocycl[3.2.2]azine derivatives. The cycloisomerization is highly stereoselective. Presence of electron donating groups on the styrenyl substituents inhibits the double cycloisomerization process and results in a trans to cis epimerization instead. No reaction takes place when electron withdrawing groups are present on the styrenyl substituents. Possible mechanisms are proposed for the observed reactions.     

meso‐N‐Pyrrole as a Versatile Substituent Influencing the Optical Properties of Porphyrin

A meso‐N‐pyrrole porphyrin converts into a π‐extended porphyrin forming an indolizine‐3‐one motif. The indolizine‐3‐one frame opens a lactam subunit preserving a six‐membered, heterocyclic structure fused with the main macrocycle. The optical properties of formed derivatives follow the structural modifications giving the absorbance and emission eventually modulated by the NH‐centered modifications of the fused unit.     

Hetarylation of indolizines

The direct incorporation of quinoline, isoquinoline, acridine, imidazole, and benzimidazole residues in the indolizine ring was accomplished by reaction of N-heteroaromatic compounds with indolizine derivatives in the presence of acylating agents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1510–1514, November, 1977.     

Crystal and molecular structure of 6-methyl-2,7-diphenyl-1,3-diformylindolizine

An x-ray crystallographic investigation was made of 6-methyl-2,7-diphenyl-1,3-diformylindolizine, obtained by the formylation of 6-methyl-2,7-diphenylindolizine. The effect of various carbonyl-containing substituents at positions 1 and 3 on the geometry of the indolizine ring in the structually investigated indolizine derivatives is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1048–1051, August, 1986.     

A reinvestigation of 4-hydroxyindole-6-carboxylate synthesis from pyrrole-2-carboxaldehyde: a facile synthesis of indoles and indolizines

Cyclization of the Stobbe product 3 under the literature conditions (acetic anhydride/sodium acetate) affords both the indole 6 and the indolizine 8. The presence of base promotes the formation of indolizine products, and using acetic anhydride/triethylamine leads to indolizine products in good yield. Improved conditions for conversion to indoles 2, 5, and 6 are reported, and inconsistencies in some of the literature structure assignments and characterization data are noted.     

Bis(oxazoline) Lewis acid catalyzed aldol reactions of pyridine N-oxide aldehydes--synthesis of optically active 2-(1-hydroxyalkyl)pyridine derivatives: development, scope, and total synthesis of an indolizine alkaloid

A new, short, and simplified procedure for the synthesis of optically active pyridine derivatives from pro-chiral pyridine-N-oxides is presented. The catalytic and asymmetric Mukaiyama aldol reaction between ketene silyl acetals and 1-oxypyridine-2-carbaldehyde derivatives catalyzed by chiral copper(II)-bis(oxazoline) complexes gave optically active 2-(hydroxyalkyl)- and 2-(anti-1,2-dihydroxyalkyl)pyridine derivatives in good yields and diastereoselectivities, and in excellent enantioselectivities-up to 99 % enantiomeric excess. As a synthetic application of the developed method, a full account for the asymmetric total synthesis of a nonnatural indolizine alkaloid is provided.