Fused Pyrrole Ring Research Articles

Theoretical descriptions on novel heteroatoms analogs of Hammick silylenes using density functional theory

AbstractIn this investigation, we have been compared and contrasted the substituent effects on stability using ΔΕs‐t (Et − Es), frequency, ΔΕHOMO‐LUMO (ELUMO − EHOMO), polarity, polarizability, Mülliken charge distribution and reactivity descriptors of the singlet and triplet Hammick silylenes derived from silapyridine‐4‐ylidene (1‐s, 2x‐s, 3x‐s and 1‐t, 2x‐t, 3x‐t; x = NH, PH, AsH, O, S, and Se) as well as the synthesized dialkylsilylenes by West (4‐s), Denk (5‐s), and Kira (6‐s). In all cases, singlet (s) silylenes appear as ground states, exhibiting more stability than their corresponding triplet (t) states. All the above s and t silylenes appear as minima on their energy surfaces showing the positive force constant and the positive harmonic vibration frequency. Regardless of how orchestrated substituent groups in either “W” or “chair” position; the most stability is demonstrated by substitution of NH, and O groups in the fused pyrrole ring, while the least stability is considered by Kira's silylene. In contrast to previous report on the N‐Heterocyclic Hammick carbenes, silylenes, and germylenes (NHCs, NHSis, and NHGes) that size, type, orientation, and the number of fused rings pronounced effect on stability of the corresponding divalent species, here σ‐donor/π‐donor groups (such as PH, AsH, S, and Se) similar to σ‐acceptor/π‐donor groups (such as NH and O) stabilize their corresponding silylenes. Furthermore, the scrutinized singlet silylenes reveal lesser nucleophilicity (N), greater electrophilicity (ω), higher chemical potential (μ), higher global hardness (η), and lower global softness (S) than the analogous triplet silylenes. All singlet and triplet species show the maximum electronic charge (ΔNmax) with positive sign.

Triazole‐fused indolo[2,3‐a]carbazoles: synthesis, structures, and properties

AbstractThe synthesis, structure, and photophysical and electrochemical properties of triazole fused indolo[2,3‐a]carbazole derivatives 2‐5 are reported. The key step involved in the synthesis of triazole fused indolo[2,3‐a]carbazole derivatives is the Cadogan ring closing reaction. 2‐Hexyl‐5,6‐dinitro‐2H‐benzo[d][1,2,3]triazoles having 4,7‐diaryl capping were subjected to the Cadogan cyclization reaction to obtain compounds 2‐5. In contrast to thiadiazole‐fused indolo[2,3‐a]carbazole 1, bromination of triazole‐fused indolo[2,3‐a]carbazole 4 afforded only meta‐dibrominated product with respect to the nitrogen of fused pyrrole rings on treatment with both N‐bromosuccinimide (NBS) and elemental bromine. These compounds showed positive solvatochromism in their emission spectra. Incorporation of electron‐donating substituent in the indole moiety resulted in the elevation of the highest occupied molecular orbital (HOMO) level. Density functional theory (DFT) calculations were performed to support the experimental findings.

One-pot synthesis of tetraarylpyrrolo[3,2-b]pyrrole dopant-free hole-transport materials for inverted perovskite solar cells

Four organic small-molecule hole transport materials (D41, D42, D43 and D44) of tetraarylpyrrolo[3,2-b]pyrroles were prepared. They can be used without doping in the manufacture of the inverted planar perovskite solar cells. Tetraarylpyrrolo[3,2-b]pyrroles are accessible for one-pot synthesis. D42, D43 and D44 possess acceptor-π-donor-π-acceptor structure, on which the aryl bearing substitutes of cyan, fluorine and trifluoromethyl, respectively. Instead, the aryl moiety of D41 is in presence of methyl with a donor-π-donor-π-donor structure. The different substitutes significantly affected their molecular surface charge distribution and thin-film morphology, attributing to the electron-rich properties of fused pyrrole ring. The size of perovskite crystalline growth particles is affected by different molecular structures, and the electron-withdrawing cyan group of D42 is most conducive to the formation of large perovskite grains. The D42 fabricated devices with power conversion efficiency of 17.3% and retained 55% of the initial photoelectric conversion efficiency after 22 days in dark condition. The pyrrolo[3,2-b]pyrrole is efficient electron-donating moiety for hole transporting materials to form good substrate in producing perovskite thin film.

Excited-State Symmetry Breaking in an Aza-Nanographene Dye.

The photophysics of a structurally unique aza-analogue of polycyclic aromatic hydrocarbons characterized by 12 conjugated rings and a curved architecture was studied in detail. The combined experimental and computational investigation reveals that the lowest excited state has charge-transfer character, in spite of the absence of any peripheral electron-withdrawing groups. The exceptionally electron-rich core comprised of two fused pyrrole rings is responsible for it. The observed strong solvatofluorochromism is related to symmetry breaking occurring in the emitting excited state, leading to a significant dipole moment (13.5 D) in the relaxed excited state. The anomalously small fluorescence anisotropy of this molecule, which is qualitatively different from what is observed in standard quadrupolar dyes, is explained as due to the presence of excited states that are close in energy but have different polarization directions.

Development of an unexpected reaction pathway for the synthesis of 1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines through palladium-catalyzed cascade reactions

1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines are synthesized through the multi-component reaction of 3-substituted 2-chloroquinoxalines, propargyl bromide, and excess secondary amines in the presence of a palladium copper catalytic system. This one-pot process provides an unexpected synthesis of new trisubstituted pyrrolo[1,2-a]quinoxalines by the introduction of two amine substituents onto the fused pyrrole rings in a single reaction procedure. The compounds formed are fully characterized by the analytical spectral data and X-ray analysis. A number of synthesized pyrrolo[1,2-a]quinoxaline derivatives are also screened against the three bacterial strains Micrococcus luteus, Pseudomonas aeruginos, and Bacillus subtilis. According to the results obtained, compounds 3b, 3c, and 3e are active against M. luteus, compounds 3b and 3e are active against Ps. Aeruginos, and only compound 3f is active against all the three bacterial strains.

Diindole[3,2-b:4,5-b′]pyrrole as a chromophore containing three successively fused pyrroles: synthesis, optoelectronic properties and π-functionalization

Diindole[3,2-b:4,5-b′]pyrrole (DIP) is an interesting chromophore containing three successively fused pyrrole rings. However, its basic properties and further π-functionalization have been rarely explored. In this article, two DIP compounds with alkyl or aromatic substituents at the central N position were successfully prepared. The preliminary optoelectronic properties of them also were studied. The property of possessing two reversible oxidation redox couples also agrees with their electron-rich nature. Similar to the alkyl case, the aromatic substitution at the central N position has subtle influence on DIP basic optoelectronic properties. Furthermore, these two compounds can be easily π-modified via the attachment of various π moieties at 2,9 or 3,8 positions of DIP skeleton. Compared with that at 2,9 positions, π-functionalization at 3,8 positions showed a much better π-extension effect.

Chemistry of Novel Non-Aromatic, Meso-Alkylidenyl Carbaporphyrinoids

We developed new class of porphyrinoids and core-modified porphyrinoids that have not been well studied previously. So called, meso-alkylidenyl porphyrins and their congeners are rather recently developed porphyrinoid family that have shown several unique properties including tautomerization, unusual protonation selectivity and spectroscopic properties. We here report the chemistry of meso-diethyl malonylidene-(m-benzi)porphyrin and meso-diethyl malonylidene-(m-benzi)pentaphyrins such the reaction with in-situ generated azomethine ylides and redox reactions. This 1,3-dipolar cycloaddition reaction has well documented and become an important alternative to the synthesis of pi-extended porphyrin analogs. The versatility and synthetic utilities associated with these reactions is useful in the synthesis of pi-extended analogs of the meso-alkylidenyl porphyrinoids. Successive 1,3-dipolar cycloaddition reaction combined with oxidation could be good tool for the pi-extended porphyrin analogs bearing region-selectively fused pyrrole rings. The 1,3-dipolar cycloaddition of the corresponding Pd(II) complexes also resulted in bis-cyclized adducts which are resistant to DDQ oxidation. All adducts are liable to core N-methylation. The adducts exhibit large bathochromic shift of absorption.

Intramolecular Schmidt reaction of tert-butyl 3-(3-azidopropyl)-4-oxopiperidine-1-carboxylate as a synthetic route to saturated fused aza heterocycles

Treatment of the title compound with trifluoroacetic acid induced intramolecular Schmidt reaction with formation of a saturated fused heterocyclic system, tert-butyl 5-oxo-2,3,4,5,7,8,9,9a-octahydro-1H-pyrrolo[1,2-a][1,4]-diazepine-2-carboxylate. The latter was reduced with lithium tetrahydridoaluminate, and subsequent treatment with hydrogen chloride in dioxane gave 2,3,4,5,7,8,9,9a-octahydro-1H-pyrrolo[1,2-a][1,4]-diazepine dihydrochloride which is a promising intermediate product for the synthesis of N-substituted diazepines with a fused pyrrole ring.

Additional Cytotoxic Pyridoacridine Alkaloids from the Ascidian Cystodytes violatinctus and Biogenetic Considerations

The extraction and purification of the bioactive extract of Cystodytes violatinctus (Solomon Islands) led to the isolation and identification of six pyridoacridine alkaloids. The structures of four new members of this family, shermilamine F (1), dehydrokuanoniamine F (2), and arnoamines C (3) and D (4), were elucidated on the basis of NMR and MS data and by comparison with data of known compounds isolated from this genus. A general hypothetical biogenetic pathway is then proposed for pyridoacridine alkaloids that contain a fused pyrrole ring. Comparison of the biological properties of the isolated alkaloids is also discussed.

Comparative photophysics of sapphyrin derivatives: effects of confused and fused pyrrole rings

We have investigated the photophysical properties of [22] π-conjugated pentapyrrolic systems, sapphyrin, N-confused and N-fused sapphyrins, with a particular focus on the effects of confused and fused pyrrole rings on their electronic structures using steady-state and time-resolved spectroscopic methods, two-photon absorption cross-section (σ(2)) measurements and quantum mechanical calculations. The absorption spectra of N-confused and N-fused sapphyrins exhibit relatively red-shifted features compared to sapphyrin. In parallel with these spectral features, the reduced HOMO–LUMO gaps were observed in going from sapphyrin to N-fused sapphyrin. In the analysis of the anisotropy of the induced current density (AICD), N-confused and N-fused sapphyrins show that extra π-electrons in confused and fused pyrrole rings contribute to the extension of their π-conjugation pathways. Slightly larger twophoton absorption cross-section values of N-confused and N-fused sapphyrins (3250 and 3900 GM) than that of sapphyrin (2900 GM) also reflect an enhanced π-conjugation effect due to bicyclic and endocyclic extensions in π-conjugation pathways, respectively. The excited singlet and triplet state lifetimes of N-confused sapphyrin were determined to be 60 ps and 1 μs, respectively, due to conformational change and acceleration of nonradiative decay processes, being in a sharp contrast with those of sapphyrin (2.4 ns and 13 μs, respectively). In the case of N-fused sapphyrin, very short singlet excited-state lifetime of 5 ps was detected probably due to the excited-state NH-tautomerization process which enhances nonradiative decay processes.

6-Methyl-2,3,4,9-tetrahydro-1H-carbazole-1-thione

In the title mol­ecule, C13H13NS, the dihedral angle between the benzene ring and the fused pyrrole ring is 0.71 (8)° and the cyclo­hexene ring is in an envelope form. The (CH2)3 atoms of the cyclo­hexene ring are disordered over two positions; the site-occupancy factor for the major component refined to 0.862 (4). In the crystal, inter­molecular N—H⋯S hydrogen bonds lead to the formation of centrosymmetric aggregates via an R 2 2(10) ring.

Transition metal mediated construction of pyrrole ring on 2,3-dihydroquinolin-4(1H)-one: synthesis and pharmacological evaluation of novel tricyclic heteroarenes

A facile two-step method for the construction of fused pyrrole ring leading to 5-substituted 2,3-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-1-ones via C-C followed by intramolecular C-N bond forming reaction is described. In vitro pharmacological evaluation and molecular modelling studies of some of the compounds synthesized are presented.

ChemInform Abstract: Novel Selective Heterocyclization of the Michael Adducts of Ene- Hydrazines with Dimethyl Acetylenedicarboxylate.

Cyclization of the Michael adducts 1 and 6 formed from ene-hydrazines and dimethyl acetylenedicarboxylate (DMAD) in the presence of polyphosphoric acid (PPA) produced the fused 1,2-diazepine rings 2 and 7. However, the adducts when heated in 1,2,3,4-tetrahydronaphthalene (tetralin) preferentially provided the fused pyridone rings 4 and 10 and the fused pyrrole rings 5 and 11.

8-Methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one

In the title compound, C13H13NO, the dihedral angle between the benzene ring and the fused pyrrole ring is 0.96 (7)°. The cyclohexenone ring adopts an envelope conformation. Inter­molecular N—H⋯O hydrogen bonds form R 2 2(10) ring motifs in the crystal structure. Weak C—H⋯π inter­actions involving the benzene ring also occur.

2-(2,3,4,9-Tetrahydro-1H-carbazol-1-ylidene)propanedinitrile

In the title mol­ecule, C15H11N3, the dihedral angle between the benzene ring and the fused pyrrole ring is 1.07 (5)°. The cyclo­hexene ring adopts an envelope conformation: the dicyano­methyl­ene group at position 1 has a coplanar orientation. An intra­molecular N—H⋯N hydrogen bond generates an S(7) ring motif. Inter­molecular N—H⋯N hydrogen bonds form an R 2 2(14) ring in the crystal. A C—H⋯π inter­action involving the benzene ring is also found in the structure.

3-Methyl-3,4-dihydro-9H-carbazol-1(2H)-one

In the title mol­ecule, C13H13NO, the dihedral angle between the benzene ring and the fused pyrrole ring is 2.03 (5)°. The methyl group at the 3-position has an equatorial orientation. The cyclo­hexene ring adopts an envelope conformation. Three C atoms of the cyclo­hexene ring, with their attached H atoms, and all atoms of the methyl group are disordered over two positions, the site-occupancy factors being 0.883 (2) and 0.117 (2). In the crystal structure, mol­ecules are stabilized by inter­molecular N—H⋯O hydrogen bonds. A C—H⋯π inter­action, involving the benzene ring, is also found.

Methyl 1-oxo-2,3,4,9-tetrahydro-1H-carbazole-2-carboxylate

In the title mol­ecule, C14H13NO3, the dihedral angle between the benzene ring and the fused pyrrole ring is 1.0 (1)°. The cyclo­hexene ring adopts a twist conformation. Three C atoms of the cyclo­hexene ring, with their attached H atoms, and all atoms of the ester group, are disordered over two positions; the site-occupancy factors are ca 0.88 and 0.12. The crystal structure is stabilized by inter­molecular N—H⋯O and C—H⋯O hydrogen bonds.

9-Methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one

The carbazole unit of the title mol­ecule, C13H13NO, is not planar. The dihedral angle between the benzene ring and the fused pyrrole ring is 2.5 (1)°. The cyclo­hexene ring is in an envelope form. There is an intra­molecular C—H⋯O hydrogen bond.

Methyl 9-methyl-1-oxo-2,3,4,9-tetrahydro-1H-carbazole-2-carboxylate

The carbazole unit of the title mol­ecule, C15H15NO3, is not planar. The dihedral angle between the benzene ring and the fused pyrrole ring is 0.53 (2)°. The cyclo­hexene ring is in half-chair form. The methyl ­acetate group at position 2 has a equatorial orientation. In the crystal structure, the mol­ecules are stabilized by inter­molecular N—H⋯O and C—H⋯O hydrogen bonds.

Structure of the Human Lung Cytochrome P450 2A13

The human lung cytochrome P450 2A13 (CYP2A13) activates the nicotine-derived procarcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) into DNA-altering compounds that cause lung cancer. Another cytochrome P450, CYP2A6, is also present in human lung, but at much lower levels. Although these two enzymes are 93.5% identical, CYP2A13 metabolizes NNK with much lower K(m) values than does CYP2A6. To investigate the structural differences between these two enzymes the structure of CYP2A13 was determined to 2.35A by x-ray crystallography and compared with structures of CYP2A6. As expected, the overall CYP2A13 and CYP2A6 structures are very similar with an average root mean square deviation of 0.5A for the Calpha atoms. Like CYP2A6, the CYP2A13 active site cavity is small and highly hydrophobic with a cluster of Phe residues composing the active site roof. Active site residue Asn(297) is positioned to hydrogen bond with an adventitious ligand, identified as indole. Amino acid differences between CYP2A6 and CYP2A13 at positions 117, 300, 301, and 208 relate to different orientations of the ligand plane in the two protein structures and may underlie the significant variations observed in binding and catalysis of many CYP2A ligands. In addition, docking studies suggest that residues 365 and 366 may also contribute to differences in NNK metabolism.