Letters in Organic Chemistry - Volume 11, Issue 6, 2014

A simple synthesis of novel benzylidenrhodanine based Furan derivatives was described from 5-arylidene 3- carboxymethylrhodanine derivatives via multi-component reactions. The reactive 1:1 intermediate produced from the reaction of tert-butyl isocyanide and dialkyl acetylenedicarboxylates was trapped at room temperature by 5-arylidene 3- carboxymethylrhodanine derivatives to yield polyfunctionalized furan rings in fairly good yields. The products have been analyzed for antibacterial activity against Gram positive and Gram negative bacteria. The results indicated that the synthesized compounds are effective against bacterial growth retardation activity to some extent and their effectiveness is higher for Staphylococcusaureus.

Electrochemical oxidation of hydroquinone and catechol derivatives (1a-1d) has been studied in the presence of 2-mercaptobenzimidazole (3) as a nucleophile in water/acetonitrile (85/15, v/v) solutions using cyclic voltammetry. Our results indicate that electrogenerated benzoquinone participated in a Michael addition reaction with 2- mercaptobenzimidazole (3) and via an EC mechanism were converted to the corresponding thioimidazole compounds. These products were obtained in good yields using a carbon electrode in an undivided cell.

A new series of 2-cyanomethylthienotriazolopyrimidines has been synthesized in good yield through a facile method using substituted aminothiophene-3-carbonitrile as building block and cyanoacetic acid hydrazide as reagent in one framework. The structure of the synthesized compounds was established on the basis of their mass and spectral data.

A water-accelerated multicomponent synthesis of organic target molecules has been used as a key method for the preparation of cyclopentadiene derivatives. The three-component condensation reactions of primary amines with alkyl propiolates in the presence of triphenylphosphine in water at 80 °C are developed as efficient and clean green synthetic procedures for the high-yielding preparation of 4-oxo-2,5-cyclopentadiene-1,2-dicarboxylate derivatives.

Sodium acetate effectively catalyzes the three component reaction between 4-nitrobenzaldehyde, malononitrile and dimedone for the formation of corresponding pyran annulated heterocyclic systems. This method offers the advantages of proceeding in neutral and mild environmental conditions, lack of toxicity, short reaction time, giving high to excellent yields of the products and simple work-up. Moreover, for the first time, an investigation of the kinetics and mechanism was made for the reaction between 4-nitrobenzaldehyde 2, malononitrile 3 and dimedone 1 compounds in the presence of sodium acetate as a catalyst. For determining the kinetics parameters of the reactions, they were monitored using UV/Vis spectrophotometery. The second order rate constant (k1) was automatically calculated by the standard equations contained within the program. In the studied temperature range, the second order rate constant depended (Lnk1, Lnk1/T) on reciprocal temperature was in good consistency with Arrhenius and Eyring equations, respectively. This data provided the suitable plots for calculating the activation energy and parameters (Ea, ΔG#, ΔS# and ΔH#) of the reaction. Furthermore, from studying the effect of solvent, concentration and catalyst on the reaction mechanism, useful information was obtained. The results showed that the first step of the reaction mechanism is a rate determining step (RDS). The mechanism which we proposed was confirmed in accordance with experimental data form UV/Vis experiment and also the steady state assumption.

The interaction of 1,3-dimethylbarbituric acid (2) with ethyl 7-chloro-1-cyclopropyl-6-fluoro-8-nitro-4- oxoquinoline-3-carboxylate (1) in basic medium yielded the respective 7-[5-(1,3-dimethylbarbitutic)]-quinoline hybrid (3). Substituted 5-bis(thioethyl)methylene barbituric acids (5a,b) underwent cyclocondensation with 7,8-diamino-6- fluoroquinoline-3-carboxylate (4) to produce the respective fluoroquinolone-benzylidene-barbiturate hybrids (6a,b) incorporating fused-imidazoline moiety. Saponification of the dimethylated ester (6b) gave the respective acid (7). The new compounds (3,5-7) show low to moderate antibacterial activity against Staphylococcus aureus and E. coli.

Treatment of 1,2-phenylenediamine with benzil analogs in the presence of a mixture of sodium bromate/ sodium hydrogen sulfite in water gave the corresponding quinoxalines in high yields. The method is eco-friendly due to use of water instead of other hazardous organic solvents.

A new piperazine-functionalized Fe3O4/SiO2 magnetite nanoparticle was synthesized through the surface modification of magnetic iron oxide nanoparticles by piperazine. Iron oxide nanoparticles were synthesized by coprecipitation method and the surface modification process was achieved by treating the nanoparticles with tetraethyl orthosilicate (TEOS), chloropropyl trimethoxy silane (CPTS) and piperazine. The developed functionalized iron oxide nanoparticle was evaluated as a reusable heterogeneous organobase catalyst for the synthesis of 4H-chromene derivatives from multi-component condensation reaction of 2-naphthol, malononitrile and aldehydes under solvent-free conditions. To receive morphological and structural information on the as-prepared catalyst, the samples were investigated by various techniques such as FT-IR, TEM, XRD, vibrating sample magnetometry (VSM), TGA and elemental analyzer. Under appropriate conditions, all reactions afforded the desired products in good to excellent yields. Moreover, this catalyst can be easily recovered by using a magnetic field and directly reused for at least six runs without significant loss of its activity.

A strategy for the synthesis of 5-substituted 1H-tetrazoles from various (E)-aldoximes and sodium azide was adopted using copper ferrite nanoparticles as a reusable catalyst.

An efficient and facile synthesis of a library of hitherto novel 1,2,3-triazolyl-pyrazoline hybrids in water medium has been achieved in excellent yields from easily accessible 1,2,3-triazole linked chalcone precursors. Herein, its noteworthy that the yield of 1,2,3-triazolyl-pyrazoline hybrids in water medium is as good as in commonly used organic solvent for pyrazoline synthesis viz. ethanol. Present protocol involving mild reaction condition, excellent yield and simple reaction procedure was found to be the best synthetic strategy for 1,2,3-triazolyl-pyrazoline hybrids in view of environmentally benign consciousness.

A mesoporous silica-supported zinc oxide catalyst was successfully synthesized by directly grinding zinc nitrate into the as-prepared Al-Containing SBA-15 occluded with template and characterized by powder X-ray diffraction (XRD), BET nitrogen adsorption-desorption methods, IR spectroscopy, transmission electron microscopy and diffuse reflectance UV-Vis spectroscopy. This solvent-free method not only saves the time and energy, but also enables a high dispersion of zinc oxide without pore blocking in the channels of mesoporous silica. The XRD and TEM analyses show that textural properties of Al-SBA-15 retained after coating process. The resulting material was successfully applied as a heterogeneous catalyst for Knoevenagel Condensation in good to excellent yields under mild conditions.

A solvent-free approach for the synthesis of a series of pyrimido[5',4':5,6]pyrido[2,3-d]pyrimidinetetraone and 4-arylacridinedione derivatives is described herein. These compounds having biological importance were prepared via a condensation reaction of aryl aldehydes, ammonium acetate and active methylene compounds including 1,3- dimethylbarbituric acid or dimedone under solvent-free conditions, using Zr(HPO4)2.H2O (α-ZrP) as an efficient catalyst. The reusability of catalyst and easier isolation of the products along with high yields of products are the advantages of this eco-friendly and versatile protocol.

The enantiomers of 9-hydroxyrisperidone, the major metabolite of risperidone and the active component of the antipsychotic drug Invega®, were synthesized by efficient methods. Their optical rotation and enantiomeric purity were characterized for the first time. The absolute configurations were assigned by comparing 1H NMR chemical shifts of Mosher esters of a key stereoisomeric intermediate. Thus, the stereoisomeric center of (+)-9-hydroxyrisperidone has been assigned as the S configuration, and its enantiomer has the configuration R.