Ragini Gupta

Microwave-assisted synthesis of nitrogen-containing heterocycles

Abstract In the recent years, microwave (MW) radiation is widely used as a source of heating in organic synthesis. Since the discovery of the MW heating approach, MW-assisted reaction has emerged as a new green-method in organic synthesis as it provides spectacular accelerations, higher yields under milder reaction conditions, and higher product purities, and it reduces pollution of the environment through the use of solvent-free reaction protocols. N-containing heterocycles hold a special place among pharmaceutically significant natural products and synthetic compounds needed for any developed human society. Therefore, organic chemists have been engaged in extensive efforts to produce these compounds following various greener techniques, primarily to circumvent growing environmental concerns. In this review, we discuss only the MW-assisted synthesis of N-containing heterocyclic compounds.

Synthesis and mass spectral studies of fluorine containing 5a, 7b, 12a, 14b-tetrahydrobisindolo [2,3-b:2′,3′-b′] benzo [1,2-d:4,5-d′] difurans

Abstract 2:1 Cycloadducts (-H 2 ) are formed when various fluorinated 2-arylindoles are stirred with p-benzoquinone in acidic medium and are identified as dimers of the type 5a, 7b, 12a, 14b-tetrahydrobisindolo [2,3-b:2′,3′-b′] benzo [1,2-d:4,5-d′] difurans. All the synthesized compounds have been characterized by their analytical and spectral (IR, PMR, 19 F NMR and Mass) data.

Eco-Friendly Synthesis and Insecticidal Activity of Some Fluorinated 2-(N-Arylamino)-4-Arylthiazoles

A series of fluorinated 2-(N-arylamino)-4-arylthiazoles (3) was synthesized by the condensation of appropriate arylthioureas (2) with corresponding α-bromoacetophenones (1) by using “green chemistry” techniques, viz. mechanochemical mixing and microwave or ultrasonic irradiation. Compared with conventional procedures, the reaction can be carried out under milder conditions, requiring a shorter reaction time and giving higher yields following the green chemistry methodology. All the synthesized compounds were characterized on the basis of elemental analyses and spectral data (IR, 1H NMR, and mass spectrometry). Representative compounds were also evaluated for their insecticidal activity against Helicoverpa armigera, and some of them showed promising activity. Supplemental materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Synthesis of Some Novel 2,3,4,8,9‐Pentahydro‐7‐(4‐haloaryl)‐pyrazolo[5,1‐e]benzo[1,5]oxazocines and 2,3(erythro), 7,8‐Tetrahydro‐2‐aryl‐3‐(4‐fluoro‐3‐methylbenzoyl)‐6‐(4‐haloaryl)pyrazolo[5,1‐d] Benzo[1,4]oxazepines via Solid–Liquid PTC

Abstract In this communication, a simple and straightforward procedure for the heterocyclization of 1H‐4,5‐dihydro‐3‐(4‐haloaryl)‐5‐substituted phenylpyrazoles (4) with 1‐bromo‐3‐chloropropane and 2,3‐dibromo‐1‐(4‐fluoro‐3‐methylphenyl)‐3‐phe‐ nylpropanone affording 2,3,4,8,9‐pentahydro‐7‐(4‐haloaryl)pyrazolo[5,1‐e]benzo[1,5] oxazocines 5 and regioselective synthesis of 2,3(erythro),7,8‐tetrahydro‐2‐ aryl‐3‐(4‐fluoro‐3‐methylbenzoyl)‐6‐(4‐halophenyl)pyrazolo[5,1‐d]benzo[1,4]oxa‐ zepines 6, respectively, via solid–liquid PTC is reported. All the synthesized compounds have been characterized on the basis of their spectral studies (IR, PMR, and MS) and analytical data.

Semiempirical calculation of diamagnetic susceptibilities of organosilicon compounds containing Si–X (X = O, S, and N) bonds

A semiempirical model is reported to calculate diamagnetic susceptibilities of organosilicon compounds containing silicon–oxygen, silicon–sulfur and silicon–nitrogen bonds. The diamagmetic susceptibilities are considered to be contributed by the atoms, bonds, and bond–bond interactions. Diamagnetic susceptibilities are expressed in terms of parameters and have been calculated for title compounds. Semiemperical values agree with experimental values within 0.75%.

Synthesis and Spectral Studies of Some New bis(1,3‐Diketonato)palladium(II) Complexes

Bis(1,3‐diketonato)palladium(II) complexes were synthesized by three routes. In route one, sodium hexachlorodipalladate in methanol was treated with the appropriately substituted diaryl‐1,3‐diketones using sodium carbonate, while in route two substituted diaryl‐1,3‐diketones were treated with palladium chloride in acetone to afford the desired bis(1,3‐diketonato)palladium(II). In route three 1,3‐bis(substituted aryl)prop‐2‐enones were treated with palladium chloride and sodium hydrogen carbonate in THF to provide the oxygen insertion product, bis(1,3‐diketonato)palladium(II) complexes. All synthesized compounds were characterized on the basis of spectral and analytical data.

Synthesis and Spectral Studies of Some Novel 2,5,9,10-Tetrahydro [7,8-g]benzo-8-arylpyrazolo[4,5-e][1,5-b]benzoxazonine via Phase Transfer Catalysis

Abstract Treatment of 1H-4,5-dihydro-3-aryl-5-(2-hydroxyaryl)pyrazole with o-dibromoxylene under liquid-liquid phase transfer catalytic conditions using tetra-n-butylammonium hydrogen sulphate or [18]-crown-6 as PT catalyst, benzene/chloroform as organic phase and 50% aqueous potassium hydroxide as second phase, afforded novel 2,5,9,10-tetrahydro [7,8-g] benzo-8-arylpyrazolo[4,5-e] [1,5-b] benzoxazonines.

Rationally designed tri-armed imidazole–indole hybrids as naked eye receptors for fluoride ion sensing

ABSTRACT The present communication describes the design, synthesis, and characterization of unique tri-armed imidazole–indole hybrids RA-RE for naked eye detection of fluoride ion in 9:1 DMSO–water at concentration level of 1.5 ppm, which is recommended permissible limit of fluoride ion. Molecular structures of the receptors are so fabricated that both heterocyclic units, namely, indole and imidazole have been rationally used as chromophore and binding unit, respectively. Strategical introduction of nitro group(s) at the fifth position of indole ring remarkably enhances the binding ability of receptor RD making it highly selective toward fluoride ion (tetrabutylammonium salt) over other typical anionic species. The sensing event can be visualized by naked eyes swiftly with color change. This observation is well corroborated by a redshift of 80 nm in UV–visible spectroscopic studies. A peak at 16.1 ppm due to in 1H NMR titration validates the deprotonation of imidazolium N‒H by fluoride ion. GRAPHICAL ABSTRACT

SYNTHESIS OF SOME 1-FLUOROARYL-1,3-DIKETONES, BIS(1,3-DIKETONATO)COPPER(II), BIS(1,3-DIKETONATO)DIOXOURANIUM(VI), AND THEIR ELECTROPHILIC SUBSTITUTION REACTIONS

Abstract Some 1-fluoroaryl-1,3-diketones were prepared by treatment of methyl 1-fluoroaryl ketone with ethyl acetate, ethyl fluoroacetate or ethyl pentafluoropropionate in the presence of sodamide which were characterized in the form of their copper chelates. 1-Substituted-aryl-1,3-diketones (1a-h) in turn on treatment with uranyl acetate afforded corresponding bis(1,3-diketonato) dioxouranium(VI) (3a-f). Bis(1,3-diketonato)dioxouranium(VI) (3a-f) when subjected to electrophilic bromination or nitration reactions yielded bis(2-bromo-1,3-diketonato)dioxouranium(VI) (4a-e) and bis(2-nitro-1,3-diketonato)dioxouranium(VI) (5a-e), respectively. The bonding mode of the ligands to the uranium ion has also been determined from IR and 1H NMR spectral studies.

Coumarin Based Receptor for Naked Eye Detection of Inorganic Fluoride Ion in Aqueous Media

Abstract In this communication, we wish to report the design, synthesis and real life applications of coumarin based “naked eye” artificial receptor for fluoride ion detection in aqueous media. Amongst easy-to-synthesize 1-(1-(substituted-2-oxo-2H-chromen-3-yl)-ethylidene)-thiosemicarbazide (receptors A-E), receptor B exhibited remarkable colour change from yellow to pink instantly upon addition of fluoride salt (sodium fluoride) 1×10-5 M (0.19 ppm), in aqueous media. Interestingly, receptor B also gave distinct and discernible colour changes perceivable even with naked eye at different fluoride ion (sodium salt) concentrations (viz., <1.5, 1.5–5 and >5 ppm) fluoride in water which allows a semi-quantitative data to be generated for fluoride contaminated drinking water. Preliminary investigation with everyday commodity items like toothpaste and mouthwash clearly show visual colour change, which may be helpful for detecting presence of fluoride in these items. This method is so simple that it has the potential for being developed as a tool for detecting different levels of fluoride in ground water, especially suitable for rural areas, where the literacy rate is low. The working pH range of receptor B was found to be 6.5–7.5. The binding constant of receptor for fluoride ion was found to be 1.38×105 M-1.