PIFA-mediated intramolecular N-arylation of 2-aminoquinoxalines to afford indolo[2,3-b]quinoxaline derivatives

We present the PIFA-mediated intramolecular N-arylation of 2-aminoquinoxalines at room temperature for the first time. This method provides a wide range of indolo[2,3-b]quinoxalines in good to excellent yields within a short time. The C-H bond functionalization occurs without the need for an inert atmosphere or additives. Additionally, a double C-H bond functionalization was observed, where the first reaction forms a C-N bond (N-arylation) and the second forms a C-O bond, yielding an acetal-functionalized product. Mechanistic investigations suggest that the C-H bond functionalization proceeds through an ionic mechanism, whereas acetal functionalization follows a radical pathway. This method extends to the derivation of indoloquinoxalines, including the target compound BIQMCz.

Metal-free construction of dihydropyrazino[2,3-b]indoles from 2-aminoacetophenones, isocyanates and 1,2-diamines

A Brønsted acid/iodine co-mediated approach to construct dihydropyrazino[2,3-b]indoles in 2-MeTHF as a green solvent at room temperature was established. A wide range of diversely substituted dihydropyrazino[2,3-b]indoles (42 examples, 61-85% yields) were synthesized under mild conditions, even on a gram scale. This protocol features organocatalysts, an eco-friendly solvent, mild conditions, readily accessible substrates, broad substrate scope and simple work-up.

Visible-Light Organophotoredox-Mediated [3 + 2] Cycloaddition of Arylcyclopropylamine with Structurally Diverse Olefins for the Construction of Cyclopentylamines and Spiro[4.n] Skeletons

We developed a visible-light-mediated [3 + 2] cycloaddition of arylcyclopropylamine with structurally diverse olefins using QXPT-NPh as a highly efficient organic photoredox catalyst. We first achieved the use of various alkyl-substituted alkenes in intermolecular [3 + 2] cycloadditions with cyclopropylamine. We also developed a general and efficient strategy for the construction of structurally diverse cyclopentane-based spiro[4.n] skeletons with 1,3-difunctional groups, which broadly exist in natural products and synthetic molecules. Furthermore, we proposed a hydrogen-bond mode between the arylcyclopropylamine and the photocatalyst QXPT-NPh.

Palladium-Catalyzed Synthesis of Heterocyclic Ring Systems by Combination of Regioselective C–C with Twofold C–N Couplings

The combination of regioselective palladium-catalyzed C–C with twofold C–N couplings allows for the synthesis of a variety of heterocyclic ring systems. Starting materials include thiophenes and benzothiophenes, pyrroles and indoles, furans and benzofurans, pyridines, quinolines and quinoxalines, complex heterocyclic systems and benzophenone derivatives. The products are in many cases complex polyheterocyclic systems, which are not readily available by other methods or, in a number of cases, were not described in the literature before. They are of pharmacological relevance or interesting in the field of material science. Products include thieno[3,2-b:4,5-b′]diindoles, thieno[3,2-b]indoles, thieno[3,4-b]indoles, 5,10-dihydroindolo[3,2-b]indoles, furo[3,2-b:4,5-b′]diindoles, benzo[4,5]furo[3,2-b]indoles, 5,7-dihydropyrido[3,2-b:5,6-b′]diindoles, 5,7-dihydropyrido[2,3-b:6,5-b´]diindoles, α-, β-, γ- and δ-carbolines, indolo[3,2-b]quinolines, indolo[2,3-b]quinolines, indolo[3,2-c]quinolines, indoloquinoxalines, pyrido[2′,1′:2,3]imidazo[4,5-b]indoles, thiadiazolo[2′,3′:2,3]imidazo[4,5-b]indoles, benzo[b]carbazolediones, acridones and thieno[3,2-b]quinolones.

Contents

1 Introduction

2 Thiophenes and Benzothiophenes

3 Pyrroles and Indoles

4 Furans and Benzofurans

5 Pyridines

6 Quinolines and Quinoxalines

7 Complex Heterocyclic Systems

8 2,3-Dibromonaphthoquinone

9 Benzophenone Derivatives

10 Conclusions

Sulfur-mediated annulation of 1,2-phenylenediamines towards benzofuro- and benzothieno-quinoxalines

We report a method for condensation between ortho-phenylenediamines and ortho-hydroxyacetophenones to afford benzofuroquinoxalines. The reactions proceeded in the presence of an elemental sulfur mediator, DABCO base, and DMSO solvent. Functionalities such as nitrile, ester, and halogen groups were compatible. The conditions could be applicable for the synthesis of benzothienoquinoxalines from ortho-chloroacetophenones.

Density functional theory, molecular docking and in vivo muscle relaxant, sedative, and analgesic studies of indanone derivatives isolated from Heterophragma adenophyllum

Heterophragma adenophyllum (HA) is an important medicinal plant which is used in traditional medicine for the treatment of muscular tension and pain. Herein, we report the isolation of methyl,1,2-dihydroxy-2-(3-methylbut-2-en-1-yl)-3-oxo-2,3-dihydro-1H-indene-1-carboxylate (1), from the roots of H. adenophyllum. The isolated compound 1 was evaluated for in vivo muscle relaxant, sedative, and analgesic potential in Swiss albino mice. Results revealed that the isolated compound 1 exhibited a dose- and time-dependent muscle coordination (51%) and a significant (p < 01) sedative effect. It also showed a considerable (p < 0.5) analgesia after 30 min of post treatment and was maintained for up-to 120 min of experimental duration. In acute toxicity studies, no mortality was observed which indicates a preliminary safety of compound 1. Furthermore, the experimental results were compared with the theoretical studies by using density functional theory (DFT). The stability of the compound as well as the flow of electrons was determined by the calculated Frontier orbital analysis. The calculated stretching frequencies, ¹H-NMR/¹³C-NMR chemical shift values and UV-visible spectra were found to be in agreement with experimental values. The results obtained from molecular docking studies were used to explore the mechanism of analgesic and muscle relaxant activity.Communicated by Ramaswamy H. Sarma.

Synthesis of Heteroannulated Indolopyrazines through Domino N-H Palladium-Catalyzed/Metal-Free Oxidative C-H Bond Activation

A convenient approach to [1,2,5]oxadiazolo[3',4':5,6]pyrazino[2,3-b]indoles and their heteroannulated analogues bearing various aryl substituents in the backbone has been developed. This synthetic protocol is based on Pd-catalyzed Buchwald-Hartwig and subsequent annulation by intramolecular oxidative cyclodehydrogenation. The photophysical properties for new polycycles have been measured.

Palladium-catalyzed synthesis and nucleotide pyrophosphatase inhibition of benzo[4,5]furo[3,2-b]indoles

A two-step palladium-catalyzed procedure based on Suzuki–Miyaura cross coupling, followed by a double Buchwald–Hartwig reaction, allows for the synthesis of pharmaceutically relevant benzo[4,5]furo[3,2-b]indoles in moderate to very good yield. The synthesized compounds have been analyzed with regard to their inhibitory activity (IC₅₀) of nucleotide pyrophosphatases h-NPP1 and h-NPP3. The activity lies in the nanomolar range. The results were rationalized based on docking studies.

Density functional theory, molecular docking and bioassay studies on (S)-2-hydroxy-N-(2S,3S,4R,E)-1,3,4 trihydroxyicos-16-en-2-yl)tricosanamide

A novel indigoferamide-A, earlier isolated from the seeds of Indigofera heterantha Wall was characterized using density functional theory, molecular docking and bioassays studies. Density functional theory calculations were performed at B3LYP/6-31G(d,p) to gain geometric insight of the compound. Conformational analyses have been performed around three important dihedral angles to explore the lowest energy structure and conformer. The simulated vibrational spectrum of the compound at B3LYP/6-31G(d,p) was scaled with two scaling factors, and the scaled harmonic vibrations shows nice correlation with the experimental values. 1H and 13C NMR chemical shifts were calculated using Cramer's re-parameterized function W04 at 6- 31G(d,p) basis set. Several conformers lying within 2 kcal mol-1 of the minimum energy conformer were considered; however, the chemical shifts were not significantly different among these conformers. The Gaussian averaged theoretical 1H and 13C chemical shifts correlate nicely with the experimental data. Electronic properties such as band gap, ionization potential and electron affinities were also simulated for the first time, however, no comparison could be made with the experiment. The compound was also screened for urease, antiglycation activities and the theoretical explanation of the results is provided based on molecular docking simulations.

Isolation, characterization and DFT studies of epoxy ring containing new withanolides from Withania coagulans Dunal

A new withanolide named as withacoagulin J (1) along with a known withanolide H (2) from Withania coagulans Dunal are reported in this paper. The isolated compounds were elucidated by using 1D-NMR (¹H NMR, ¹³C NMR) and 2D-NMR including homonuclear (COSY, NOESY) and heteronuclear (HSQC, HMBC); along with Mass spectrometry, UV-Visible and IR spectroscopic techniques. The molecular formula based on Fast-Atom Bombardment Mass Spectrometry [FAB-MS (M + 1)] for 1 and 2 were deduced as C₂₈H₃₇O₅ and C₂₈H₃₉O₆ with m/z values 453.2624 and 471.6041, respectively. The quantum mechanical studies of both compounds are based on DFT calculations. The DFT studies show band gaps of 4.86 and 4.83 eV for 1 and 2, respectively. The band gaps of 1 and 2 reflect high stability and resistivity towards oxidation-reduction reactions. The energies of HOMO and LUMO for compound 1 are -6.11 and -1.25 eV and for compound 2: -6.47 and -1.64 eV respectively. Theoretical and experimental FTIR data closely match for both the compounds which support the high accuracy of the computational protocol selection. Other parameters such as bond lengths, bond angles and dihedral angles for both compounds are also studied.

Pyrazinoindole-Based Lewis-Acid/Base Assembly: Intriguing Intramolecular Charge-Transfer Switching through the Dual-Sensing of Fluoride and Acid

Pyrazinoindole-based Lewis-acid/base assemblies are prepared through the use of regioselective formal [3 + 3] cycloaddition reactions, and their intriguing photophysical properties are described. The assemblies exhibit strong emissions in THF solution, which are attributed to through-space intramolecular charge-transfer (ICT) transitions between the branched Lewis-acid/base moieties. Furthermore, these show ratiometric color-change responses in PL titration experiments, which give rise to new colors through turn-on emissions ascribable to ICT transitions that alternate between the pyrazinoindole units and each triarylboryl or amino moiety, a consequence of the binding of the fluoride or acid. Pieces of filter paper covered by these assemblies exhibited blue-shifted color changes when immersed in aqueous acidic solutions, suggesting that these are promising candidate indicators that detect acid through emissive color. Computational data for these assemblies and their corresponding adducts verify the existence of ICT transitions that alternate through fluoride or acid binding.

Synthesis of furo[3,2-b:4,5-b']diindoles and their optical and electrochemical properties

An efficient two-step palladium catalyzed synthesis of furo[3,2-b:4,5-b']diindoles, a hitherto unknown symmetrical heterocyclic core structure, was developed. The synthesis is based on a regioselective Suzuki-Miyaura cross coupling reaction of tetrabromofuran and subsequent double N-arylation. Selected compounds were studied with regard to their optical and electrochemical properties. The compounds show fluorescence with high quantum yields and non-reversible oxidation events. The compounds possess similar HOMO-LUMO band gaps compared to their sulfur and nitrogen analogs. Variation of the substituents hardly affects the HOMO-LUMO gap, but allows for some fine-tuning of the electron affinity and ionization potential as well as quantum yields. The compounds prepared represent interesting candidates for the development of organic electronic materials.

Synthesis, Spectral Characterization and Fluorescent Assessment of 1,3,5-Triaryl-2-pyrazoline Derivatives: Experimental and Theoretical Studies

Two new pyrazoline derivatives, namely 5-(4-bromophenyl)-3-(5-chlorothiophen-2-yl)-1-phenyl-4,5-dihydro-1H-pyrazole (3) and 5-(4-bromophenyl)-3-(2,5-dichlorothiophen-3-yl)-1-phenyl-4,5-dihydro-1H-pyrazole (4) have been synthesized and characterized based on their spectral (IR, (1)H and (13)C NMR and MS) data and microanalysis. The fluorescence properties of 3 and 4 were studied by UV-Vis and emission spectroscopy. For compound 3, a fluorescence emission was observed in the blue region of the visible spectrum. The effect of different solvents on fluorescence was also investigated. Density Functional Theory calculations have also been performed to gain insight into geometric, electronic and spectroscopic properties of the pyrazoline derivatives. Both structures are analysed and compared in order to rationalize the different behaviour in 3 and 4.

Spectroscopic and density functional theory studies of 7-hydroxy-3'-methoxyisoflavone: A new isoflavone from the seeds of Indigofera heterantha (Wall)

A new isoflavone 7-hydroxy 3'-methoxyisoflavone (1) is isolated from the seeds of Indigofera heterantha. The structure of this new compound was established using spectroscopic techniques such as ID, 2D NMR, and mass spectrometry. Density functional theory calculations are carried out for the first time for geometric, electronic and spectroscopic properties of 1 (isoflavone). DFT calculations have been performed at B3LYP/6-311G(d,p) level of theory for obtaining geometric and spectroscopic properties of compound 1. The simulated vibrational spectrum of compound 1 at B3LYP/6-311G(d,p) shows nice correlation with the experimental IR spectrum after a scaling factor of 0.973. (1)H and (13)C NMR chemical shifts were calculated using Cramer's re-parameterized function WP04 at 6-311G(d,p) basis set, and show nice correlation with the experimental data. Four conformers were considered for NMR chemical shift calculations. Electronic properties such as band gap, Ionization potential and electron affinities were also simulated for the first time; however, no comparison could be made with the experiment.

Isolation, spectroscopic and density functional theory studies of 7-(4-methoxyphenyl)-9H-furo[2,3-f]chromen-9-one: a new flavonoid from the bark of Millettia ovalifolia

The phytochemical examination of chloroform soluble fraction (FX2) of methanolic extract of bark of Millettia ovalifolia yielded a new flavonoid; 7-(4-methoxyphenyl)-9H-furo [2,3-f]chromen-9-one (1). Compound 1 is characterized by spectroscopic analytical techniques such as UV, IR, 1D, 2D NMR spectroscopy, and mass spectrometry. A theoretical model is also developed for obtaining geometric, electronic and spectroscopic properties of 1. The geometry optimization and harmonic vibration simulations have been carried out at B3LYP/6-31G(d,p). The vibrational spectrum of compound 1 shows nice correlation with the experimental IR spectrum, through a scaling factor of 0.9613. (1)H and (13)C NMR chemical shifts are simulated using Cramer's re-parameterized function WP04 at 6-31G(d,p) basis set, and correlate nicely with the experimental chemical shifts.

Towards thermally stable cyclophanediene-dihydropyrene photoswitches

Cyclophanediene dihydropyrenes (CPD-DHP) are photochromic compounds because they change their color by irradiation with lights of different color. Potential use of CPD-DHP photoswitch in memory devices requires a very slow thermal return in the dark in the absence of any side reaction. Herein, thermal return of CPDs to DHPs, and an unwanted sigmatropic shift in DHP is studied through density functional theory calculations at (U)B3LYP/6-31+G(d). The thermal return occurs through symmetry forbidden conrotatory electrocyclic reaction. Dimethyl amino CPD-DHP photoswitch pair has the highest activation barrier for electrocyclization and sigmatropic shifts. The lowest activation barrier for symmetry forbidden electrocyclization is observed for GeBr3 functionalized CPD. An unprecedented decomposition pathway involving elimination of the internal substituents is predicted for Cl, Br and SMe functionalized DHPs. This study shows great promise in understanding the Woodward Hoffmann forbidden processes and, in reducing the synthetic efforts toward robust photochromes for memory applications.

Synthesis, crystal structures and spectroscopic properties of triazine-based hydrazone derivatives; a comparative experimental-theoretical study

We report here a comparative theoretical and experimental study of four triazine-based hydrazone derivatives. The hydrazones are synthesized by a three step process from commercially available benzil and thiosemicarbazide. The structures of all compounds were determined by using the UV-Vis., FT-IR, NMR (¹H and ¹³C) spectroscopic techniques and finally confirmed unequivocally by single crystal X-ray diffraction analysis. Experimental geometric parameters and spectroscopic properties of the triazine based hydrazones are compared with those obtained from density functional theory (DFT) studies. The model developed here comprises of geometry optimization at B3LYP/6-31G (d, p) level of DFT. Optimized geometric parameters of all four compounds showed excellent correlations with the results obtained from X-ray diffraction studies. The vibrational spectra show nice correlations with the experimental IR spectra. Moreover, the simulated absorption spectra also agree well with experimental results (within 10–20 nm). The molecular electrostatic potential (MEP) mapped over the entire stabilized geometries of the compounds indicated their chemical reactivates. Furthermore, frontier molecular orbital (electronic properties) and first hyperpolarizability (nonlinear optical response) were also computed at the B3LYP/6-31G (d, p) level of theory.

Synthesis of indolo[1,2-f]phenanthridines by Pd-catalyzed domino C–N coupling/hydroamination/C–H arylation reactions

Indolo[1,2-f]phenanthridines were prepared by Pd-catalyzed domino C–N coupling/hydroamination/C–H arylation reactions.

Efficient synthesis of α- and δ-carbolines by sequential Pd-catalyzed site-selective C–C and twofold C–N coupling reactions

Two concise and efficient approaches were developed for the synthesis of α- and δ-carboline derivatives.

Novel synthesis of 5-methyl-5,10-dihydroindolo[3,2-b]indoles by Pd-catalyzed C–C and two-fold C–N coupling reactions

A series of 5,10-dihydroindolo[3,2-b]indoles was successfully prepared by an efficient two-step strategy.