Intercepted-Knoevenagel condensation for the synthesis of unsymmetrical fused-tricyclic 4H-pyrans

4H-Pyrans (4H-Pys) and 1,4-dihydropyridines (1,4-DHPs) are important classes of heterocyclic scaffolds in medicinal chemistry. Herein, an indium(III)-catalyzed one-pot domino reaction for the synthesis of highly functionalized 4H-Pys, and a model of 1,4-DHP is reported. This alternative approach to the challenging Hantzsch 4-component reaction enables the synthesis of fused-tricyclic heterocycles, and the mechanistic studies underline the importance of an intercepted-Knoevenagel adduct to achieve higher chemoselectivity towards these types of unsymmetrical heterocycles.     

Colorimetric determination of sinalbin

Summary Sinalbin (Sinapinp-hydroxybenzylglucosinolate) is present in white mustard seed(sinapis alba) and on enzymatic hydrolysis liberates a sharp, hot, pungent and flavoury compound,p-hydroxybenzyl isothiocyanate (p-HBI). A new sensitive colorimetric method has been developed in which thep-HBI is reacted with sodium hydroxide to givep-hydroxybenzyl alcohol and sodium thiocyanate. The thiocyanate is converted into cyanogen bromide by reacting it with bromine. The cyanogen bromide is then treated with pyridine—benzidine reagent to give a red colour which has an absorption maximum at 518 nm. The red complex solution obeys Beer's law over the concentration range 0.1–0.5 g of SCN per ml of the solution. One mole of sinalbin gives rise to one mole of thiocyanate ion. Recovery is 90%.

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Zusammenfassung Sinalbin (Sinapin-p-hydroxybenzylglucosinolat) ist ein Inhaltsstoff des Samens von weißem Senf (Sinapis alba) und bildet bei enzymatischer Hydrolyse eine scharf schmeckende, würzig riechende Verbindung, p-Hydroxybenzyl-isothiocyanat (p-HBI). Ein neues kolorimetrisches Verfahren wurde entwickelt, das auf der Reaktion von p-HBI mit Natronlauge beruht, wobei p-Hydroxybenzylalkohol und NaCNS entstehen. Dieses wird mit Brom zu Bromcyan umgesetzt, das seinerseits mit Pyridin-Benzidin eine Rotfärbung mit dem Absorptionsmaximum bei 518 nm gibt. Die Lösung dieser roten Komplexverbindung folgt dem Beer'schen Gesetz von 0,1–0,5 g SCN^–/ml. Ein Mol Sinalbin entspricht einem Grammion Thiocyanat. Die Ausbeute beträgt etwa 90%.

     

Vibrational spectroscopic studies of an organic non-linear optical crystal 8-hydroxyquinolinium picrate

8-hydroxyquinolinium picrate (8-HQP) was synthesized by the addition of equimolar quantities of 8-hydroxyquinoline (8-HQ) and picric acid (PA). Single crystals were grown from N,N dimethyl formamide (DMF) by restricted evaporation method at room temperature. The solubility of 8-HQP was determined in different solvents at various temperatures. The structural characterization of the grown crystals was carried out by X-ray diffraction. Vibrational modes were classified on the basis of group theoretical analysis and the spectral bands were compared with those of parent compounds in order to propose a tentative assignment by recording FT-IR, FT-Raman and polarized Raman spectra in different crystal orientations. The crystal possess lower cut-off at 230 nm and good transparency as confirmed by optical transmittance studies.     

Design,synthesis and in vitro antibacterial activities of methyl-4-((substituted phenyl)[6H-indolo(2,3-b)quinoxalin-6-yl]methyl-amino)benzoate derivatives

A series of new methyl-4-((substituted phenyl)[6H-indolo(2,3-b)quinoxalin-6yl]methylamino)benzoate derivatives have been synthesized and assayed for their antibacterial activity on 9 different bacterial strains.Among the screened compounds 2e-2g exhibited potent inhibitory activity compared to standard drug employed,worth further investigation.     

Catalytic effect of CTAB reverse micelles on the kinetics of dissociation of bis(2,4,6–tripyridyl-s-triazine) iron(II)

The kinetics of dissociation of bis(2,4,6–tripyridyl-s-triazine) iron(II), ([Fe(TPTZ)₂]²⁺) has been studied in CTAB/chloroform/hexane reverse micellar medium. In the absence of acid, the reaction is immeasurably slow and does not go to completion in conventional aqueous medium but is markedly accelerated and takes place with a rate constant equal to 55.3 × 10^?3 s^?1 and goes to completion in reverse micelles. The significant increase in rate is attributed to the special properties of the water pool in the reverse micelles like low dielectric constant, nucleophilic effect of Br^- ion, and favorable partitioning of TPTZ in the organic phase. The rate of the reaction decreases with increase in W (=[H₂O]/[CTAB]) at constant CTAB concentration and remains constant with increase in CTAB at fixed W. The results are compared with other closely related systems.     

Studies on vibrational, dielectric, mechanical and thermal properties of organic nonlinear optical co-crystal: 2,6-diaminopyridinium-4-nitrophenolate-4-nitrophenol

This article presents the vibrational, dielectric, mechanical and thermal properties of 2,6-diaminopyridine-4-nitrophenolate-4-nitrophenol co-crystals (DAP:NP) grown by slow evaporation solution growth technique. It crystallizes in orthorhombic noncentrosymmetric space group Pna2₁ with cell dimension a=10.86 Å, b=12.00 Å and c=13.53 Å; α=β=γ=90° with V=1764 Å³. Functional groups present in the molecule have been identified from FTIR study. Dielectric constant (ε_r), dielectric loss (tanδ) and ac conductivity (σ_ac) behaviors of the crystals have been studied at different temperatures. Presence of piezoelectric resonance peaks at lower frequency in dielectric measurements may increase the electro-optic coefficient of the crystals. Mechanical strength and its parameters of the grown crystals have been determined by Vickers microhardness test. TG/DTA analysis shows the melting point of the material is 150 °C and it undergoes two stages of decomposition.     

Mechanistic investigation and implications of a sacrificial aniline for the tandem cascade synthesis of 4-aza-podophyllotoxin analogues

Mechanistic investigations were pursued to determine a plausible mechanism in the cascade reaction involving tetronic acid with aldehydes and anilines to generate the 4-aza-2,3-dehydropodophyllotoxin core structure. The mechanistic driven hypothesis paved the way for a new reaction design using for the first time a sacrificial electron deficient aniline leading to an optimized cascade protocol (up to threefold yield improvement) for the synthesis of novel 4-aza-2,3-dehydropodophyllotoxin analogues.     

Growth and spectroscopic characterization of a new organic nonlinear optical crystal--8-hydroxyquinoline

A novel organic nonlinear optical crystal 8-hydroxyquinoline having good optical quality has been grown by slow evaporation solution technique using methanol as solvent. The morphology of the grown crystals were identified by X-ray diffraction method. Solubility studies were made under various solvents and solvent mixtures at different temperatures. Functional groups present in the grown material have been identified using FTIR and FT Raman spectra. Transparency was tested using UV-vis spectrophotometer and the second harmonic generation was also verified.