Nature Of Substituents Research Articles

Differentiation between Isomeric 4,5-Functionalized 1,2,3-Thiadiazoles and 1,2,3-Triazoles by ESI-HRMS and IR Ion Spectroscopy.

A large variety of 1,2,3-thiadiazoles and 1,2,3-triazoles are used extensively in modern pure and applied organic chemistry as important structural blocks of numerous valuable products. Creation of new methods of synthesis of these isomeric compounds requires the development of reliable analytical tools to reveal the structural characteristics of these novel compounds, which are able to distinguish between isomers. Mass spectrometry (MS) is a clear choice for this task due to its selectivity, sensitivity, informational capacity, and reliability. Here, the application of electrospray ionization (ESI) with ion detection in positive and negative modes was demonstrated to be useful in structural studies. Additionally, interconversion of isomeric 4,5-functionalized 1,2,3-triazoles and 1,2,3-thiadiazoles was demonstrated. Application of accurate mass measurements and tandem mass spectrometry in MS2 and MS3 modes indicated the occurrence of gas-phase rearrangement of 1,2,3-triazoles into 1,2,3-thiadiazoles under (+)ESI-MS/MS conditions, independent of the nature of substituents, in line with the reaction in the condensed phase. Infrared multiple photon dissociation (IRMPD) spectroscopy enabled the establishment of structures of some of the most crucial common fragment ions, including [M+H-N2]+ and [M+H-N2-RSO2]+ species. The (-)ESI-MS/MS experiments were significantly more informative for the sulfonyl alkyl derivatives compared to the sulfonyl aryl ones. However, there was insufficient evidence to confirm the solution-phase transformation of 1,2,3-thiadiazoles into the corresponding 1,2,3-triazoles.

Photochemical production of molecular hydrogen in the presence of substituted acridine salts

The photocatalytic properties of new representatives of the family of metal-free catalysts, 10-hydro-9-phenylacridine, 10-methyl-9-phenylacridinium chloride, and 10-phenyl-9-phenylacridinium chloride, were studied with respect to the reaction of molecular hydrogen generation in the presence of acids of different strength (HClO4, CH3SO3H, and CF3COOH) and reducing agents ([Bu4N]Cl, [Bu4N]Br, and [Bu4N]I). It was found that the strength of acids (p K a) and the nature of the reducing agent ( E 0) significantly affect the efficiency, i.e. turnover frequency (TOF), of the process under study. The amount of formed molecular hydrogen reaches its maximum in the case of the combination HClO4 and [Bu4N]I, characterized by minimal p K a and E0 values, respectively. The influence of the nature of substituents at the nitrogen atom in 9-phenylacridine on the efficiency of the molecular hydrogen production was analyzed. It was shown that the limiting stage of the process is the protonation of the formed radical.

Regioselective Cycloaddition of Nitrile Imines to 5-Methylidene-3-phenyl-hydantoin: Synthesis and DFT Calculations.

Nitrile imine cycloaddition to hydantoins containing an exocyclic C=C double bond has been previously described in a very limited number of examples. In this work, regioselective synthesis of spiro-pyrazoline-imidazolidine-2,4-diones based on a 1,3-dipolar cycloaddition reaction of nitrile imines to 5-methylidene-3-phenyl-hydantoin have been proposed. It was found that, regardless of the nature of the aryl substituents at the terminal C and N atoms of the C-N-N fragment of nitrile imine (electron donor or electron acceptor), cycloaddition to the 5-methylidenhydantoin exocyclic C=C bond proceeds regioselectively, and the terminal nitrogen atom of the nitrile imine connects to the more sterically hindered carbon atom of the double bond, which leads to the formation of a 5-disubstituted pyrazoline ring. The observed cycloaddition regioselectivity was rationalized using DFT calculations of frontier molecular orbital interactions, global CDFT reactivity indices, and minimum energy paths.

Rational design of efficient photosensitizers based on cyclometalated iridium(III) complexes with 2-arylbenzimidazole and aromatic 1,3-diketone ligands.

A judicious selection of substituents in cyclometalating 2-arylbenzimidazoles and an ancillary aromatic 1,3-diketone enabled the creation of heteroleptic iridium(III) complexes demonstrating strong light absorption up to 500 nm (ε ≈ 10 000-12 000 M-1 cm-1). The complexes, which were studied by various spectroscopic techniques, single-crystal X-ray diffraction and cyclic voltammetry, displayed tunable absorption maxima depending on the nature of substituents and their positions. The experimental study was corroborated by quantum chemical calculations, which showed an increased contribution of intraligand charge transfer transitions to the visible light absorption in the case of complexes containing electron-withdrawing substituents in the ligands. Despite being of high intensity, some of these transitions are responsible for the formation of the excited states located at large distances from the 'anchoring' fragment incorporated in the ancillary ligand. In turn, incorporation of electron-donating substituents at the para-position to the Ir-C bonds increases the number of excited states located on the ancillary ligand. The destabilization of the HOMO, which is caused by the increase in the electron-donating ability of the substituents in the metalated rings, translated into negative shifts of the Ir4+/Ir3+ redox potential, affecting, in some cases, the degree of electrochemical reversibility of the complexes. Several complexes having strong light-harvesting characteristics and undergoing reversible oxidation in the appropriate potential range were used for coating the TiO2 photoanodes, which reached an efficiency of 2.15% upon irradiation with the standard AM 1.5 spectrum.

Scope and limitations of absolute configuration determination of allenic natural products using the CCC stretching VCD signal.

The allene functional group in natural products isolated so far exists in a non-racemic form, but its axial chirality is difficult to elucidate. Allenes exhibit a characteristic antisymmetric CCC stretching mode at around 1950 cm-1, and their VCD properties have not been studied in detail. This work, for the first time, applied VCD spectroscopy to allenic natural products and allenic molecules with other asymmetric centers focusing on the antisymmetric CCC stretching mode. This vibrational mode yielded a negligibly weak VCD signal for several molecules, but in the presence of electron-withdrawing and/or conjugating substituents, it generated a stronger one. Its sign was found to be influenced by the nature of substituents. These findings should deepen the understanding of the VCD properties of the allene functional group and should be useful for future studies of chiral allenes.

Investigating the mechanism of Ni-mediated trifluoromethylthiolation of aryl halides using AgSCF3.

The mechanism of the Ni-catalysed trifluoromethylthiolation of aryl chlorides using AgSCF3 is studied herein. A variety of IPr NiII complexes were synthesized via oxidative addition of Ni0 to 2-(2-chloro)phenylpyridines. Their reactivity with AgSCF3 was tested by performing stoichiometric experiments, cyclic voltammetry, and NMR spectroscopic studies. CuSCF3 was shown to behave similarly to AgSCF3, while reactions with NMe4SCF3 revealed a major stoichiometric side reaction that forms a nickel fluoride complex. NMR kinetic studies revealed there is little correlation between the electron-withdrawing/donating nature of the para substituents on either the phenyl or pyridyl groups with the formation of the corresponding products. Cyclic voltammetry (CV) indicated the feasibilty of NiI/NiIII transitions, and an increased rate of formation of product was observed with increased solvent polarity. Evidence suggests that the mechanism proceeds via inner-sphere electron transfer (ET) from AgSCF3 to NiII, ultimately leading to the formation of the trifluoromethylthiolated product.

Effect of Nature of Substituents on Coordination Properties of Mono- and Disubstituted Derivatives of Boron Cluster Anions [BnHn]2– (n = 10, 12) and Carboranes with exo-Polyhedral B–X Bonds (X = N, O, S, Hal)

This review systematizes data on the coordination ability of mono- and disubstituted derivatives of boron cluster anions and carboranes in complexation with transition metals. Boron clusters anions [BnHn]2–, monocarborane anions [CBnHn–1]–, and dicarboranes [C2BnHn–2] (with non-functionalized carbon atoms) (n = 10, 12) containing the B–X exo-polyhedral bonds (X = N, O, S, Hal) are discussed. Synthesis and structural features of complexes known to date are described. The effect of complexing metal and substituent attached to the boron cage on the composition and structures of the final complexes is analyzed. It has been established that substituted derivatives of boron cluster anions and carboranes can act as both ligands and counterions. A complexing agent can coordinate substituted derivatives of the boron cluster anions due to three-center two-electron 3c2e MHB bonds, by the substituent functional groups, or a mixed type of coordination can be realized, through the BH groups of the boron cage and the substituent. As for B-substituted carboranes, complexes with coordinated substituents or salts with non-coordinated carborane derivatives have been isolated; compounds with MHB bonding are not characteristic of carboranes.

Solid Lipid Nanoparticles Based on Monosubstituted Pillar[5]arenes: Chemoselective Synthesis of Macrocycles and Their Supramolecular Self-Assembly

Novel monosubstituted pillar[5]arenes with one or two terminal carboxyl groups were synthesized by the reaction of succinic anhydride with pillar[5]arene derivative containing a diethylenetriamine function. The ability for non-covalent self-assembly in chloroform, dimethyl sulfoxide, as well as in tetrahydrofuran-water system was studied. The ability of the synthesized macrocycles to form different types of associates depending on the substituent nature was established. The formation of stable particles with average diameter of 192 nm in chloroform and of 439 nm in DMSO was shown for pillar[5]arene containing two carboxyl fragments. Solid lipid nanoparticles (SLN) based on monosubstituted pillar[5]arenes were synthesized by nanoprecipitation in THF-water system. Minor changes in the structure of the macrocycle substituent can dramatically influence the stability and shape of SLN (spherical and rod-like structures) accordingly to DLS and TEM. The presence of two carboxyl groups in the macrocycle substituent leads to the formation of stable spherical SLN with an average hydrodynamic diameter of 364-454 nm. Rod-like structures are formed by pillar[5]arene containing one carboxyl fragment, which diameter is about of 50-80 nm and length of 700-1000 nm. The synthesized stable SLN open up great prospects for their use as drug storage systems.

Photochromism of tetrahydroindolizines. Part XXVI: Mechanochemical synthesis, tunable photophysical properties and combined experimental and theoretical studies of novel photochromic tetrahydroindolizines

Herein, eighteen novel photochromic tetrahydroindolizines (THIs) have been successfully prepared using a well-established mechanochemical synthetic approach. These products were obtained in good to excellent yields and the purification process was relatively straightforward devoid of any isolation challenges. The new THIs incorporate various substituents in region C (base part) which include both electron donating and withdrawing groups in the ortho, meta and para positions of the phenyl ring. The absorption maxima (λmax) of both closed form (THI) and the colored form (betaine, after UV-irradiation) were spectrophotometrically determined in dichloromethane solution. The colored betaines displayed two absorption maxima, one between 472 and 485 nm, and the second one appearing in the white region between 658 and 724 nm with tailing extending to the near infra-red (NIR) region. The impact of the nature and position of substituent in the 10′b-phenyl ring on the absorption of the betaines indicated that substitution in the ortho-position with absorption maxima between 658 and 690 nm leads to a hypsochromic shift largely caused by the steric effect of the substituents in the o-position of the THI molecule 10′b-phenyl ring compared to the meta- and para-substituted species with absorption maxima between 700 and 724 nm. The calculated ring closure thermodynamic activation parameters of colored betaines were found to be in good agreement with previous reported results. The 1,5-electrocyclization reaction kinetics of the investigated photochromic THIs were monitored and calculated. Intriguingly, substitution with electron donating and withdrawing groups in the o-, m-, and p-positions of the phenyl ring enabled distinctive tunability of the kinetic behavior. Furthermore, possible mechanism of the thermal 1,5-electrocyclization back reaction of betaines was explored based on density functional theory calculations (DFT), delivering more understanding into ring opening and ring closure processes in addition to the distinct THI-substituents effect (region C). The geometries and the relative energies of the THI, betaine isomers, and transition states along reaction coordinates were optimized and assessed by DFT. Based on the obtained synthetic methodology results, unprecedent tunability of the photochromic properties and the combined experimental and theoretical studies, the current work launches a new dimension and contributes further developments to the field of high-performance photochromic materials.

Nitration of 2,6,8,12-Tetraacetyl-2,4,6,8,10,12-Hexaazaisowurtzitane Derivatives.

The nitration of novel bioactive derivatives of 2,6,8,12-tetraacetyl-2,4,6,8,10,12-hexaazaisowurtzitane in different nitrating systems was examined. The yield of CL-20, the known product from the nitration of hexaazaisowurtzitane compounds, was found to depend on the nature of substituents at the 4,1 positions and on the composition of the nitrating mixture.

Excited-State Modification of Phenylimidazole-Based Cyclometalated Ir(III) Complexes through Secondary Bulky Aryl Substitution and Inductive Modification Enhances the Blue Emission Efficiency in Phosphorescent OLEDs

To elucidate the key parameters governing the emission properties of phenylimidazole (pim)-based Ir(III) emitters, including their electronic structure and the bulky aryl substitution effect, a series of pim-based iridium(III) complexes (Ir(Rpim-X)3, Rpim-X = 1-R-2-(X-phenyl)-1H-imidazole) bearing secondary pendants of increasing bulkiness [R = methyl (Me), phenyl (Ph), terphenyl (TPh), or 4-isopropyl terphenyl (ITPh)] and three different primary pim ligands (X = F, F2, and CN) were designed and synthesized. Based on photophysical and electrochemical analyses, it was found that the excited state properties are highly dependent on the bulkiness of the secondary substituent and the inductive nature of the primary pim ligand. The incorporation of bulky TPh/ITPh substituents in the second coordination sphere significantly enhanced the emission efficiencies in the solid state (ΦPL = 72.1-84.9%) compared to those of the methyl- or phenyl-substituted Ir(III) complexes (ΦPL = 30.4% for Ir(Mepim)3 and 63.7% for Ir(Phpim)3). Further modification of the secondary aryl substituent (Ir(TPhpim)3 → Ir(ITPhpim)3) through the incorporation of an isopropyl group and F substitution on the primary pim ligand (Ir(TPh/ITPhpim)3 → Ir(TPh/ITPhpim-F/F2)3) resulted in a slight decrease in the LUMO and a significant decrease in the HOMO energy levels, respectively; these energy level adjustments consequently amplified emission blue shifts, thereby enabling efficient blue electroluminescence in phosphorescent organic light-emitting diodes. Theoretical calculations revealed that the excited-state properties of pim-based Ir(III) complexes can be modulated by the nature of the peripheral substituent and the presence of an EWG substituent. Among the fabricated blue-emitting TPh/ITPh-substituted Ir(III) complexes, Ir(ITPhpim-F)3, Ir(TPhpim-F2)3, and Ir(ITPhpim-F2)3 were tested as blue-emitting dopants for blue phosphorescent OLEDs owing to their high solid radiative quantum yields (ΦPL = 75.9-84.9%). The Ir(ITPhpim-F)3-doped multilayer device displayed the best performance with a maximum external quantum efficiency of 21.0%, a maximum current efficiency of 43.6 cd/A, and CIE coordinates of 0.18 and 0.31.

Synthesis, Structure and Photochemistry of Dibenzylidenecyclobutanones.

A series of symmetrical dibenzylidene derivatives of cyclobutanone were synthesized with the goal of studying the physicochemical properties of cross-conjugated dienones (ketocyanine dyes). The structures of the products were established and studied by X-ray diffraction and by NMR and electronic spectroscopy. All the products had E,E-geometry. The oxidation and reduction potentials of the dienones were determined by cyclic voltammetry. The potentials were shown to depend on the nature, position, and number of substituents in the benzene rings. A linear correlation was found between the difference of the electrochemical oxidation and reduction potentials and the energy of the long-wavelength absorption maximum. This correlation can be employed to analyze the properties of other compounds of this type. Quantum chemistry was used to explain the observed regularities in the electrochemistry, absorption, and fluorescence of the dyes. The results are in good agreement with the experimental redox potentials and spectroscopy data.

Expanding the Chemical Space of Drug-like Passerini Compounds: Can α-Acyloxy Carboxamides Be Considered Hard Drugs?

With their three points of diversity, α-acyloxy carboxamides, which are accessible with the Passerini reaction, provide heterogeneity for the preparation of libraries of putative active agents or intermediates used for the formation of more complex structures. If on the one hand the presence of a hydrolyzable ester function has been exploited to design both prodrugs and soft drugs, on the other hand medicinal chemists are reluctant to use this skeleton to prepare hard drugs. Herein we investigated whether the stability of the ester could be controlled, leading to the formation of hydrolytically stable α-acyloxy carboxamides. When the group directly attached to the ester moiety (R3) is an ortho-substituted or ortho,ortho'-disubstituted aromatic ring, α-acyloxy carboxamides are stable. In human liver but not in rodents, due to the different expression of esterases, the ester function is also stable toward hydrolysis when the R1 group is a bulky substituent regardless of the nature of the R3 substituent.

Novel Complexes of 3-[3-(1H-Imidazol-1-yl)propyl]-3,7-diaza-bispidines and β-Cyclodextrin as Coatings to Protect and Stimulate Sprouting Wheat Seeds.

We report the syntheses and characterization of novel 3,7-bicycl[3.3.1]bispidines possessing an imidazolpropyl group attached to N-3, and at N-7 a Boc group, as well as a benzoylated-oximated group at C-9. These compounds were complexed with β-cyclodextrin [β-CD] and evaluated as seed protectors of selected wheat seedlings. Using strong acid, condensations of N-substituted piperidones with the appropriate imidazolpropyl groups at N-3 and N-7 led to bispidinones 6 and 7. These intermediates were reduced to the corresponding 3,7-diazabicyclo[3.3.1]nonane targets. The oxime at C-9 was benzoylated to yield 13. Heating these 3,7-diazabicyclo[3.3.1]nonanes in ethanol with β-CD generated the complexes required. We investigated the ability of such complexes as coatings on seedlings to protect and stimulate growth of three varieties of wheat, namely Kazakhstanskaya-10, Severyanka, and Miras. The complex of 3-[3-(1H-imidazol-1-yl)propyl]-7-(3-methoxypropyl)-3,7-diazabicyclo[3.3.1]nonane (2) promoted growth in the root systems of all three wheat varieties by more than 30% in Kazakhstanskaya-10, 30% in Severyanka and 8.5% in Miras. A complex of 3-Boc-7-[3-(1H-imidazol-1-yl)propyl]-3,7-diazabicyclo[3.3.1]nonane (9) increased both shoot and root length in only the Severyanka variety. The complex of 3-(3-butoxypropyl)-7-[3-(1H-imidazol-1-yl)propyl]-3,7-diazabicyclo[3.3.1]nonane (11) stimulated both shoot growth (0.8%, 12.3%, 13.5%) and root growth (12.3%, 9.4%, 21.7%) in all three varieties of wheat, respectively. The nature of substituents on the bispidine affect the activity. Solid complexes (1:1) were generated as powders which melted above 240 °C (dec) and were characterized via elemental analyses as 1:1 complexes.

DOS strategy, crystal structure, and in silico evaluation of the anti‐inflammatory activity of hydroxysulfanylazole derivatives

We developed a DOS approach to the synthesis of hydroxysulfanylazole derivatives (12 examples) using diversification with various N,N- and N,O-binucleophilic reagents of the carbonyl groups of hydroxysulfanyl diketones (6 examples) obtained by the piperidine-catalyzed thiomethylation reaction involving the С(α)-Н position of 2,4-pentanedione with aromatic aldehydes and 2-mercaptoethanol. X-ray diffraction analysis was used to determine the structures and crystal packing for three hydroxysulfanylpyrazoles. The calculation of the intermolecular interactions in the crystals (analysis of Hirshfeld surfaces) demonstrated the influence of the substituent nature on the contribution of the H…O/O…H contacts. Using molecular docking studies, justified assumptions were made about the complementarity of the obtained series of compounds to the active sites of COX isoforms.

Synthetic Nanoarchitectonics of Functional Organic-Inorganic 2D Germanane Heterostructures via Click Chemistry.

Succeeding graphene, 2D inorganic materials made of reactive van der Waals layers, like 2D germanane (2D-Ge) derivatives, have attracted great attention because their physicochemical characteristics can be entirely tuned by modulating the nature of the surface substituent. Although very interesting from a scientific point of view, almost all the reported works involving 2D-Ge derivatives are focused on computational studies. Herein, a first prototype of organic-inorganic 2D-Ge heterostructure has been synthesized by covalently anchoring thiol-rich carbon dots (CD-SH) onto 2D allyl germanane (2D-aGe) via a simple and green "one-pot" click chemistry approach. Remarkably, the implanted characteristics of the carbon nanomaterial provide new physicochemical features to the resulting 0D/2D heterostructure, making possible its implementation in yet unexplored optoelectronic tasks-e.g., as a fluorescence resonance energy transfer (FRET) sensing system triggered by supramolecular π-π interactions-that are inaccessible for the pristine 2D-aGe counterpart. Consequently, this work builds a foundation toward the robust achievement of functional organic-inorganic 2D-Ge nanoarchitectonics through covalently assembling thiol-rich carbon nanoallotropes on commercially available 2D-aGe.

QSRR DESCRIPTORS AS A TOOL IN THE STUDY OF THE BARBITURIC ACID DERIVATIVES’ BIOLOGICAL PROFILE

Thanks to the in silico approach in drug design, the identification of new molecules is enabled and facilitated, as well as the optimization of the pharmacokinetics and toxicity of compounds obtained from different sources. Chromatographic methods, on the other hand, provide accurate and reliable information on the influence of the nature of substituents and applied organic modifiers on the pharmacological behavior of compounds, relying on the existence of similarities between intermolecular interactions that determine compound behavior in biological and chromatographic media. Barbituric acid derivatives were subjected to QSRR analysis and the parameters obtained by reversed phase thin layer chromatography (RP TLC18 F254s) were correlated with selected software-derived predictors of permeability, pharmacokinetics and toxicity using the method of linear regression. Тhus satisfactory mathematical models were obtained.

Assessing p-tolyloxy-1,3,4-oxadiazole acetamides as lipoxygenase inhibitors assisted by in vitro and in silico studies

The underlying correlation between the inflammation, innate immunity and cancer is extensively familiar and linked through a process mediated by three enzymes; cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (CYP450). The ever increase in the reported side effects of the antiinflammatory drugs against the targeted enzymes and the resistance developed afterwards compels the researchers to synthesize new effective molecules with safer profile. On the basis of these facts, our ongoing research on 1,3,4-oxadiazole derivatives deals with the synthesis of a new series of N-alkyl/aralky/aryl derivatives of 5-((p-tolyloxymethyl)-4H-1,3,4-oxadiazole-2-ylthio)acetamide (6a-o) which were developed by the sequential conversion of p-tolyloxyacetic acid (a) into ester (1) hydrazide (2) and 5-(p-tolyloxymethyl)-4H-1,3,4-oxadiazole-2-thiol (3). The designed compounds (6a-o) were acquired by the reaction of 1,3,4-oxadiazole (3) with numerous electrophiles (5a-o) in KOH. The synthesized analogues (6a-o) were characterized by FTIR, 1H-, 13C NMR spectroscopy, EI-MS and HR-EI-MS spectrometry, and were further assessed for their inhibitory potential against the soybean 15-LOX enzyme. The results showed excellent inhibitory potential of the compounds against the said enzyme, specifically 6o, 6b, 6n and 6e with inhibitory values (IC50 ± SEM) of 21.5 ± 0.76, 24.3 ± 0.45, 29.1 ± 0.65 and 31.3 ± 0.78 µM, respectively. These compounds displayed < 55 % blood mononuclear cells (MNCs) cellular viability as measured by MTT assay at 0.25 mM concentration. Other compounds demonstrated moderate inhibitory activities with IC50 values in the range of 33.2 ± 0.78 to 96.3 ± 0.73 µM and exhibited little cellular viability against MNCs except 6i, 6j, 6 m and 6 k that showed 61–79 % cellular viability. It was observed that most of the compounds (6o, 6b, 6n, 6e) were found more toxic towards MNCs at studied concentration of 0.25 mM. SAR studies revealed that the positions and nature of substituents accompanying phenyl ring have great influence on 15-LOX inhibitory activity. In the most active compound 6o, the amino acids Asp768 and Val126 were involved in hydrogen bonding, Thr529 was linked with π-anion interaction and π-sulphur interaction was displayed with Tyr525 and two π-alkyl interactions were formed with the benzene ring and amino acid residues Pro530 and Arg533. The in silico pharmacokinetics profiles and density functional theory calculations of the compounds further supported the in vitro findings. Further work on the synthesis of more oxadiazole derivatives is in progress in search for potential ‘leads’ for the drug discovery as LOX inhibitors.

In-depth analysis of the photophysics of BOPAHY dyes in solution, glass and film

BOPAHY dyes are a recently synthesized class of asymmetric highly fluorescent double boron complexed dyes. The photophysics of 5-substituted BOPAHY dyes was investigated by steady-state and time-resolved spectroscopy in liquid solution, dissolved in an organic glass and in neat spin-coated films. In the latter samples some derivatives show efficient fluorescence. The experimental results were compared with the predictions from DFT and time dependent DFT. The influence of the nature of the hetero-aromatic substituent in the 5-position on the features of the absorption and fluorescence spectra and the decay of the S1-state is linked to the molecular morphology. The experiments show the choice of the 5-substituent is critical to avoid loss of a boron center in solution.

Synthesis of 3-benzylquinoxalin-2(1H)-ones and 4-formyl-3-benzyl-3,4-dihydroquinoxalin-2(1H)-ones from 3-aryloxirane-2-carboxamides via 5-arylidene-2,2-dimethyl-1,3-oxazolidin-4-ones

A facile and highly efficient strategy has been delineated for the synthesis of 3-benzylquinoxalin-2(1H)-ones and their partially reduced N-formyl derivatives via a Hinsberg-Körner type cyclo-annulation reaction using 5-arylidene-2,2-dimethyl-1,3-oxazolidin-4-ones as pyruvate surrogates. 3-Benzylquinoxalin-2(1H)-ones with a wide range of substituents in both the benzyl moiety and the quinoxaline ring are formed in good to excellent yields and are easily converted into partially reduced N-formyl derivatives when boiled in a mixture of formic acid and formamide (1:1). The method features are mild condition, easy work-up (a simple filtration), practicality and robustness, excellent tolerance to the nature of substituents in starting compounds.