N-Silatranylmethyl Derivatives of Pyrrole,Indole, and Carbazole

Organosilicon derivatives of pyrrole, indole, carbazole, and 2-methylindole containing (MeO)₃SiCH₂, Et₃SiCH₂, or N(CH₂CH₂O)₃SiCH₂ group on the nitrogen atom were synthesized. Their structure and stereoelectronic parameters were studied by X-ray diffraction, ¹H, ^{1 3}C, ^{1 5}N, and ^{2 9}Si NMR, IR and UV spectroscopy, and dielcometry, as well as by quantum-chemical calculations.     

无溶剂自催化合成吡咯或吲哚Michael加成产物

在吡咯或吲哚自身N－H的催化下,在无溶剂条件下合成了3个吡咯和5个吲哚Michael加成产物(2a～2c和3a～3e,其中2b和3a～3e为新化合物),收率80%～92%, 3a~3c的d/r值分别为3.8 : 1, 1.3 : 1和1.1 :1,其结构经¹H NMR, ¹³C NMR, IR和HR-MS(ESI)表征。     

Triflic Acid–Catalyzed Michael Reactions of Indole and Pyrrole Compounds with α,β‐Unsaturated Ketones in Water

The Michael reactions of indole and pyrrole compounds to α,β‐unsaturated ketones catalyzed by triflic acid (HOTf, 0.1–1 mol%) were performed in water to give alkylated indoles (3a–m) and dialkylsubstituted pyrroles (6a–b) in good to excellent yields.     

Highly Enantioselective Synthesis of β‐Heteroaryl‐Substituted Dihydrochalcones Through Friedel–Crafts Alkylation of Indoles and Pyrrole

A highly enantioselective Friedel–Crafts (F–C) alkylation of indoles and pyrrole with chalcone derivatives catalyzed by a chiral N,N′‐dioxide–Sc(OTf)₃ complex has been developed that tolerates a wide range of substrates. The reaction proceeds in moderate to excellent yields and high enantioselectivities (85–92 % enantiomeric excess) using 2 mol % (for indole) or 0.5 mol % (for pyrrole) catalyst loading, which showed the potential value of the catalyst system. Meanwhile, a strong positive nonlinear effect was observed. On the basis of the experimental results and previous reports, a possible working model is proposed to explain the origin of the activation and asymmetric induction.     

Synthesis and Cytotoxic Evaluation of Pyrrole Hetarylazoles Containing Benzimidazole/Pyrazolone/1,3,4‐Oxadiazole Motifs

Azomethine‐linked pyrrole bishetarylazoles containing benzimidazole/pyrazolone/1,3,4‐oxadiazole were synthesized in satisfactory yields. Their structures were confirmed by IR, ¹H‐NMR, ¹³C‐NMR, and elemental analysis. Evaluation for the cytotoxic activities in vitro against a panel of breast cancer cell lines (MDA‐AB‐231, BT‐474, and Ishikawa cells) revealed that the pyrrole–benzimidazole hybrids are more potent than the pyrazolone and 1,3,4‐oxadiazole hybrids in all cell lines. Compound 9 displayed promising cytotoxicity against BT‐474 cell line with IC₅₀ values, 7.7 µM.     

Single and Consecutive Cyclization Reactions of Alkynyl Carbene Complexes and 8‐Azaheptafulvenes: Direct Access to Polycyclic Pyrrole and Indole Derivatives

The reactivity of alkynyl and enynyl Fischer carbene complexes towards 8‐azaheptafulvenes is examined. Alkynyl carbenes 1 a – f undergo regioselective [8+2] heterocyclization with 8‐aryl‐8‐azaheptafulvenes 2 a , b providing cycloheptapyrroles 3 and 4 with metal carbene or ester functionality at C3. Moreover, consecutive cyclization reactions are involved when enynyl carbenes are used. Thus, the cyclopenta[b]pyrrole framework 7 is formed by the consecutive [8+2] cyclization and cyclopentannulation reactions. The initially formed cyclopentannulation adduct can be intercepted through a Diels–Alder reaction with classic dienophiles to afford increasing structural complexity (compounds 8 and 9 ). More importantly, the construction of the indole skeleton is accomplished with a high degree of substitution and functionalization (compounds 11 – 15 ) by a one‐pot sequence that involves [8+2] cyclization, R? NC or CO insertion, and ring closure.     

Formation of the 5-Azoniafulvene Ion and its Benzo-annellated Analogue from N-Mannich Bases of Pyrrole and Indole

1-Dialkylaminomethylpyrroles are shown to behave in many respects like aminals. Acylation by an acid chloride, for instance, occurs normally at the amine-type N-atom rather than at the pyrrole ring. Spontaneous cleavage of the resulting quaternary acylammonium salts affords the 5-azoniafulvene ion ( 3 ). This higly reactive iminium ion, and its benzo-annellated analogue ( 4 ) can be trapped by electron rich aromatic compounds such as N-methylpyrrole or N,N-dimethylaniline. More elaborate N-Mannich bases are accessible by addition of indoles to enamines.     

Rational Design,Synthesis and Evaluation of Indole Nitrogen Hybrids as Photosystem II Inhibitors

We report the synthesis of twelve indole derivatives bearing nitro or amide groups via Fischer indole methodology followed by reduction/acetylation and amidation reactions. After thorough characterization, these indoles were subjected to a number of studies in order to evaluate their bioactive potential as photosynthesis and plant growth inhibitors. Firstly, these molecular hybrids were evaluated as photosystem II (PSII) inhibitors through chlorophyll a (Chl a) fluorescence measurement. In this study, 6-chloro-8-nitro-2,3,4,9-tetrahydro-1H-carbazole ( 15a ) and 5-chloro-2,3-dimethyl-7-nitro-1H-indole ( 15b ) showed the best results by reducing the phenomenological parameters of reaction centers ABS/RC, TR₀/RC and ET₀/RC of PSII. Electron chain blockage by these compounds may lead to diminished ATP synthesis and CO₂ fixation which interrupt the plant development. The compounds 15a and 15b both act as postemergent herbicides, reducing the dry biomass of Ipomoea grandifolia and Senna alata weeds by an average of 40% and 37%, respectively, corroborating the fluorescence results. Additionally, the molecular docking study revealed that the presence of strong electron-withdrawing groups at the indole phenyl ring is important for the ligand’s interaction with the binding pocket of protein D1 on PSII. The optimization of these molecular features is the goal of our research group in further understanding and development of new potent herbicides.     

New chemical reactivity in aromatic dithiocarbamate and monothiocarbamate ligands: syntheses of Mo2L4·2THF (L = Pyrrole or indole monothiocarbamate or pyrrole dithiocarbamate) and Mo2L4 (L = indoline monothiocarbamate)

The reactions between Mo₂(C₂H₃O₂)₄ and several new dithio- and monothiocarbamates have been studied. The first example of a dimolybdenum compound of a dithiocarbamate with the “molybdenum acetate” structure is reported (Mo₂L₄·2THF; L = pyrrole dithiocarbamate). In addition, the synthesis of Mo₂L′₄·2THF (L′ = pyrrole monothiocarbamate, indole monothiocarbamate, indole dithiocarbamate) and Mo₂L″₄ (L″ = indoline monothiocarbamate) are reported. A discussion of the unique stabilization of the dithiocarbamate bridge by “aromatic” dithio- and monothiocarbamates is presented.     

Confinement inside a Crystalline Sponge Induces Pyrrole To Form N−H⋅⋅⋅π Bonded Tetramers

Based on the DFT-level-calculated molecular volume (V_mol) of pyrrole and its liquid density, pyrrole manifests the highest liquid density coefficient LD_c (defined as [V_mol×density ×0.6023]/FW) value of 0.7. Normal liquids have LD_c <0.63. This very high LD_c is due to the strong N−H⋅⋅⋅π interactions in solution, and hence pyrrole can be considered to be a pseudo-crystalline liquid. When trapped inside the confined space of a crystalline sponge, a reorientation of the N−H⋅⋅⋅π interaction is observed leading to specific cyclic N−H⋅⋅⋅π tetramers and N−H⋅⋅⋅π dimers, as verified by single-crystal X-ray crystallographic and computational methods. These tetramers are of the same size as four pyrrole molecules in the solid-state of pyrrole, yet the cyclic N−H⋅⋅⋅π intermolecular interactions are circularly oriented instead of being in the linear zigzag structure found in the X-ray structure of a solid pyrrole. The confinement thus acts as an external driving force for tetramer formation.     

An Electrochemical Investigation into a Series of Tricyanovinylated Pyrrole Moieties

The electrochemical behavior of three tri‐cyanovinylated pyrrole species namely, 2‐tricyanovinyl‐pyrrole (C₄H₄N? C₅N₃), 2‐tricyanovinyl‐N‐methylpyrrole (C₅H₆N? C₅N₃) and 2‐tricyanovinyl‐N‐phenylpyrrole (C₁₀H₈N? C₅N₃), has been studied. All compounds were found to exhibit both an irreversible oxidation at more positive potentials compared to the unsubstituted monomer species and a reversible reduction redox couple associated with reduction of the co‐ordinated cyano ligands. The latter reductions of the tricyanovinylated compounds to their radical anions at platinum, carbon and gold electrodes in acetonitrile solution have been studied by cyclic voltammetry, using a variety of supporting electrolytes. The half‐wave potentials for each compound were found to be dependent upon the supporting electrolyte but independent of the nature of the electrode surface. This is attributed to ion‐pairing between the anions and the alkali metal cations. The reduction based redox processes of C₁₀H₈N? C₅N₃ and C₅H₆N? C₅N₃ were found to be facile in nature and independent of both the nature of the electrolyte and electrode surface. However, the reduction of C₄H₄N? C₅N₃ was found to be irreversible in nature. Attempts were made to elucidate, by both electrochemical and spectroscopic means, the structure of the products obtained upon oxidation of the tricyanovinylated compounds.     

Indole derivatives

The influence of dehydrogenating dehydrating (deaminating) additives on the composition and yield on the products of the cyclization of N-(-hydroxyethyl)aniline and N,N-diphenylethylenediamine has been studied. The closure of the indole and pyrrole rings takes place through the dehydration and deamination, respectively, of the starting material on oxide catalysts. A reaction scheme explaining the formation of all the products observed has been suggested.For Communication L see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 6, pp. 766–769, June, 1970.     

An Apparent Umpolung Reactivity of Indole through [Au]-Catalysed Cyclisation and Lewis-Acid-Mediated Allylation

The sequential functionalization of indole C2 and C3 in an umpolung fashion was executed with a predesigned substrate and choice of reagents. The developed method comprises gold-catalysed alkynol cycloisomerisation/intramolecular addition of C2 of indole and subsequent BF₃ ⋅ OEt₂-mediated regioselective C3 allylation, resulting in the synthesis of the functionalized indoloisoquinolinone scaffold. The reaction involves 5-endo-alkynol cycloisomerisation and the dearomative addition of indole C2 to the intermediate oxocarbenium cation, which results in two equilibrating fused and spiropentacyclic intermediates, which upon treatment with allyl silane in the presence of BF₃ ⋅ OEt₂, undergo selective indole C3 allylation. Other nucleophiles, such as hydride, azide and indole, were also found to be compatible with this process.     

A New Indole Alkaloid from Cleome droserifolia

The phytochemical investigations on Cleome droserifolia resulted in the isolation and characterization of a new indole alkaloid, 5‐hydroxy‐2‐methoxy‐1‐methyl‐1H‐indole‐3‐carbaldehyde ( 1 ). The structure elucidation was carried out on the basis of 1D‐ and 2D‐NMR techniques. In addition to 1 , two known aromatic derivatives, veratrol ( 2 ) and 2‐methoxy‐4‐methylacetophenone ( 3 ), were also obtained. All these compounds were purified by repeated column chromatography of the CH₂Cl₂ fraction obtained from MeOH extract of Cleome droserifolia. The structure of the new compound 1 was finally confirmed by the combined 1D (¹H‐ and ¹³C‐) and 2D (H? C correlations; HMBC and HSQC) NMR and IR spectroscopy, mass spectrometry (MS), and UV absorption spectroscopy techniques. The comparison of the physical and spectroscopic data with those in the literature provided evidence for the structure confirmation of known compounds. All the purified compounds were subjected to urease and α‐glucosidase enzymes inhibition. The results showed that compound 1 was more potent with an IC₅₀ value 11.97±2.067 μg/ml towards urease inhibition, while the activity of α‐glucosidase enzyme was marginal.     

Monoterpenoid Indole Alkaloids Bearing an N4‐Iridoid from Gelsemium elegans

Five new alkaloids, gelseganines A–D ( 1 – 4 ) and humantenine N₄‐oxide ( 5 ), were isolated from the stems and leaves of Gelsemium elegans. Compounds 1 – 4 represent a rare class of monoterpenoid indole alkaloids that bear an N₄‐iridoid unit. The structures of 1 – 5 were determined by spectroscopic analysis, single‐crystal X‐ray diffraction, and chemical correlation, and their absolute configurations were elucidated by CD analysis. A plausible biogenetic pathway for alkaloids 1 – 5 was also postulated.     

Addition reactions of heterocycles. VII. Pyrrole and C-Acetyl-N-phenylnitrilimine

The addition reaction of C-acetyl-N-phenylnitrilimine to pyrrole has been investigated. The products obtained show that the reaction proceeds via two distinct pathways. The 1,3-addition reaction leads to the non-cyclic-adduct III, whereas the 1,3-cycloaddition reaction gives a mixture of regioisomeric Δ₂-pyrroline IV and V, and Δ₁ -pyrroline VI and VII mono-cycloadducts. These latter compounds cannot be isolated because they undergo a further 1,3-cycloaddition reaction leading to the N-substituted bis-adducts X and XI, and to the bis-adduets XII and XIII. The stereochemical assignment for X, XI, XII and XIII is provided by nmr data which suggest also that in X and XI the rotation around the exocyclic N-C bond is relatively slow on the instrument time scale.     

Synthesis and Electrochemical Polymerisation of Calix[4]pyrroles Containing N-substituted Pyrrole Moieties

Abstract

The first examples of the synthesis of calix[4]pyrroles containing pendant N-substituted pyrrole moieties (in the meso- (2) and β- (1) positions) is reported. Attempts at the production of electropolymerised films containing (1) or (2) alone failed, however the electrochemical co-polymerisation of (1) and pyrrole and (2) and pyrrole has been achieved.     

Synthesis of novel fused azaheterocycles by photostimulated intramolecular SRN1 reactions with nitrogen nucleophiles

The synthesis of pyrrole, indole, and pyrazole fused azaheterocycles is presented. The anions of carboxamides (6 and 12) and pyrazolylamines (15a-b) react under photostimulation by an intramolecular S_RN1 process to yield fused azaheterocycles with good to excellent yields. We report on an efficient two-step synthesis of new fused azaheterocycles derived from pyrrole, indole, and pyrazole, as well as the synthesis of their precursors. By the reaction of carboxamides (6 and 12) and pyrazolylamines (15a-b) with a base, the corresponding anion could be formed. Then, by an intramolecular photostimulated S_RN1 reaction, the fused azaheterocycles were achieved (54-100%).     

吡咯和呋喃气相质子化过程的密度泛函理论研究

Density functional theory and ab initio calculations have been used to determine structures and stabilities of the protonated aromatics species AH^＋ and AH2^2＋ （A=pyrrole, furan）. Possible mechanisms and relative energetics for protonation of pyrrole and furan by H3O^＋ and AH^＋ in the gas phase have been explored. Calculations show that the Cα-protonated species was the most stable structure for AH^＋, and the protonated AH^＋ might accommodate the second proton to yield AH2^2＋ if the free proton was available. The gas-phase H3O^＋ could protonate pyrrole and furan with significant exothermiCity and almost without barrier. The proton transfer from AH4^＋ to pyrrole and furan has a barrier ranging from 33.5 to 39.3 kJ/mol in the gas phase.     

Anti‐inflammatory Activity of Two New Indole Alkaloids from the Stems of Nauclea officinalis

Two new indole alkaloid derivatives ( 1 , 2 ), together with six known indole alkaloids ( 3  –  8 ) were isolated from the 70% EtOH/H₂O extract of the stem of Nauclea officinalis. Their structures were determined on the basis of extensive analyses of spectroscopic data (IR, MS, 1D‐ and 2D‐NMR). All the isolates were evaluated for their anti‐inflammatory activities on lipopolysaccharide (LPS)‐induced nitric oxide (NO) production in RAW 264.7, and all the compounds showed significant inhibitory activities with the IC₅₀ values of 0.82, 6.45, 9.75, 1.34, 3.40, 2.69, 1.58, and 1.96 μm , compared to the positive drug control group aminoguanidine with an IC₅₀ value of 1.80 μm , especially compound 1 had the most significant activity.