Domino routes to substituted benzoindolizines: tandem reorganization of 1,3-dipolar cycloadducts of nitrones with allenic esters/ketones and alternative cycloaddition-palladium catalyzed cyclization pathway

Reactions of C-(4-oxo-4H[1]benzopyran-3-yl)-N-phenyl nitrones (7) with allenic esters (8a-c) and allenic ketones (18a-d) furnish benzoindolizines (9a-k, 19a-d) in good yields. The formation of benzoindolizines is postulated to involve regioselective addition of 1,3-dipole to C2-C3 π bond of allenic esters/ketones followed by domino transformation of the cycloadducts, which involve an intramolecular aza Diels-Alder reaction in the intermediate C. DFT calculations of various parameters for diene and dienophile components in the proposed intermediate C have revealed that conformational constraints imposed by the alkyl groups (R=Me, Et) favor intramolecular aza-Diels-Alder cycloaddition. An alternative domino route to benzoindolizines (9a,d,g) involving sequential one-pot cycloaddition of azadienes (22a-c) with silyl-enol ether (23) followed by palladium(0)-catalyzed Heck coupling reaction has also been developed. Both these approaches represent novel domino routes for the synthesis of benzoindolizines.     

Solvent and substituent effects on the photoreduction of cobalt(III)-aryl amine complexes in an aquo-organic solvent medium

The photoreduction of a series of Co^III complex ions, [Coen₂Cl(RC₆H₄NH₂)]²⁺ where R = p-OMe, p-OEt, p-Me, m-Me, H, and p-F, has been studied using a low pressure Hg vapour lamp as the light source (254 nm) in an aquo-organic solvent [15–40% (v/v) 2-methylpropan-2-ol] medium. Quantum yields for Co^II production by redox decomposition have been determined in all cases. The quantum yield increases considerably with the increase in concentration of the organic co-solvent in the binary solvent mixture under investigation. The Hammett correlation is linear, affording negative reaction constants, which indicate that the excited state is electron deficient. Correlation of the experimental results with Kamlet–Taft's solvatochromic parameters indicates that the solvent hydrogen bond donor acidity plays a dominant role in governing the reactivity.     

Preparation of nitrogen-doped reduced graphene oxide and its use in a glassy carbon electrode for sensing 4-nitrophenol at nanomolar levels

We describe a novel procedure for the synthesis of nitrogen-doped reduced graphene oxide (N-rGO). It is based on the thermal reduction of GO (dispersed in water) with sodium diethyldithiocarbamate that acts as both the reducing agent and the source for nitrogen. The surface morphology of the N-rGO is characterized using high resolution transmission electron microscopy. X-ray photoelectron spectroscopy was carried out to study the composition of their surface, and Raman spectroscopy was performed to study the level of doping with nitrogen and the structural order. The N-rGO was deposited on a glassy carbon electrode (GCE), and the resulting electrode utilized as a sensing platform for 4-nitrophenol (4-NP). The modified GCE exhibits a well-defined oxidation peak current that is about ten times larger when compared to that of a bare GCE. The electron transfer number, proton transfer number and electron transfer rate constant (k_s 1.046 s^?1) were determined. At optimized conditions, the oxidation peak current is linearly related to the concentration of 4-NP in the 20–500 nM range, with a correlation coefficient of 0.9917. The detection limit (at an SNR of 3) is 7 nM. The method was successfully applied to the analysis of waters spiked with 4-NP. Recoveries range from 97.8 to 102.6 %, and no interferences are found for common inorganic cations and anions. Figure

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α-Fe2O3@carbon core–shell nanostructure for luminescent upconversion and photocatalytic degradation of methyl orange

Research on Chemical Intermediates - The unique characteristics of metal–organic frameworks such as structural tunability, high surface area, low density, and tailored porosity have made this...     

Solvent hydrogen bonding and structural effects on nucleophilic substitution reactions: Part 3. Reaction of benzenesulfonyl chloride with anilines in benzene/propan‐2‐ol mixtures

Substitution reactions of 13 para‐ and meta‐substituted anilines with benzenesulfonyl chloride in varying mole fractions of benzene in propan‐2‐ol have been investigated conductometrically. The second‐order rate constants correlate well with pK_a values of anilines and with the Hammett's equation. The negative Hammett reaction constant indicates the formation of an electron‐deficient transition state. The rate data correlate satisfactorily with macroscopic solvent parameters such as relative permittivity, ε_r, and polarity, E_T^N. Correlation of rate data with Kamlet–Taft solvatochromic parameters (α, β, π*) suggests that both the specific and nonspecific solute–solvent interactions influence the reactivity. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 657–663, 2007     

Solvent and substituent effects on the electrochemical oxidation of para‐ and meta‐substituted anilines

Electrochemical oxidation of 15 para‐ and meta‐substituted anilines in different mole fractions of water in 2‐methylpropan‐2‐ol has been investigated in the presence of 0.1 M sulfuric acid as a supporting electrolyte. The oxidation potential data of anilines correlate well with the Brown–Okamoto's substituent constants affording a negative reaction constant. The effect of para‐ and meta‐substituents on the oxidation potential confirms to Swain's F and R, affording negative reaction constants. The oxidation potential values also correlate satisfactorily with macroscopic solvent parameter such as relative permittivity, ε_r. The results of Kamlet–Taft multiple correlation analysis show that specific solute–solvent interactions play a dominant role in governing the reactivity. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 289–297, 2007     

Oxidation of substituted benzaldehydes by quinolinium chlorochromate: A structure and solvent dependent kinetic study

The kinetics of oxidation of several para‐substituted benzaldehydes by quinolinium chlorochromate was studied under pseudo‐first‐order conditions in different (hydrogen bond donor and hydrogen bond acceptor) neat organic solvents. The operation of nonspecific and specific solvent–solvent–solute interactions was explored by correlating the rate data with solvent parameters through correlation analysis. Both electron‐releasing and electron‐withdrawing substituents enhanced the rate and the Hammett plot showed a break in the reactivity order indicating applicability of dual mechanism. An explanation in conformity with structure and solvent effects on reactivity has been proposed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 154–158, 2003     

Spectroscopic studies on the dynamics of charge‐transfer interaction of pantoprazole drug with DDQ and iodine

Spectrophotometric method was used to study the kinetics of charge‐transfer (CT) complexes of pantoprazole with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and iodine. The reactions of DDQ and iodine with pantoprazole have been investigated in different solvents at three different temperatures. The products of the interactions have been isolated and characterized using UV–vis, GC‐MS, FT‐IR, and far‐IR spectral techniques. The rate of formation of the product has been measured and discussed as a function of solvents and temperature. The iodine complex indicates the formation of the tri‐iodide CT complex with a general formula [(PTZ)I]⁺I. The characteristic strong absorptions of I are observed around 360 and 290 nm in the electronic spectra, and the far‐IR spectrum exhibits three characteristic vibrations of I unit at 156, 112, and 69 cm^?1 assigned to ν_as(I‐I), ν_s(I‐I), and δ(I), respectively. The activation parameters (ΔG^#, ΔS^#, and ΔH^#) were obtained from the temperature dependence of the rate constants. The influence of relative permittivity of the medium on the rate indicated that the intermediate is more polar than the reactants, and this observation was further well supported by spectral studies. Based on the spectrokinetic results, plausible mechanisms for the interaction of the drug with the chosen acceptors, which proceed via the formation of CT complexes and its transformation into final products, have been proposed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 787–799, 2009     

Chilenine: An isoindolobenzazepine alkaloid

(±)-Chilenine ($\text{3}$), the first isoindolobenzazepine alkaloid, has been found in $\text{Berberis}$$\text{empetrifolia}$ Lam. (Berberidaceae).