Synthesis and Studies of Symmetrical DitelluraCalix[6]phyrin(1.1.1.1.1.1)s.

Rare examples of ditellura calix[6]phyrin(1.1.1.1.1.1)s containing two telluratripyrrin units connected via two sp3 carbons were synthesized by condensing 16-telluratripyrrane with a cyclic ketone in CH2Cl2 under acid-catalyzed conditions. The X-ray structure obtained for meso-cyclohexyl-substituted calix[6]phyrin revealed that the macrocycle resembles a roof-like shape with two telluratripyrrin units that are perpendicular to each other, whereas the DFT-optimized structure of meso-cyclopentyl-substituted calix[6]phyrin showed a bird-like structure with two telluratripyrrin units that are almost in the same plane.

Unravelling the Metal Sensing Activity of a Biologically Relevant Fluorescent Crown Ether: A Unified Experimental and Theoretical Study.

1,4-dihydropyridines (DHPs) are biologically active. 1,4-DHP analogs with appropriate substituents also show characteristic fluorescence activity. Here, for the first time, we report a simple and easy synthesis of a novel fluorescent 1,4- DHP derivative of dibenzo[18]-crown-6 (2), which showed promising sensing ability towards physiologically important metal ions. The covalent linking of 1,4-DHP analog with dibenzo[18]-crown-6 instigates its fluorescence activity in (2) and makes it biologically relevant. (2) shows a noteworthy enhancement of fluorescence intensity toward Fe3+ and Ba2+ in methanol medium. DFT studies revealed that metal binding by the crown ether-O atoms leads to structural rigidity, enhancing the fluorescence intensity. Interestingly, (2) shows utility in the quantitative detection of Fe3+ ions in the biological (human blood serum) and food samples.

Synthesis and Studies of Mono-functionalized Telluradithiasapphyrins and Covalently Linked Porphyrin- Telluradithiasapphyrin Dyads.

A series of mono-functionalized aromatic 22π telluradithiasapphyrins containing functional groups such as p-bromophenyl, p-iodophenyl, p-nitrophenyl and p-trimethylsilylethynyl phenyl groups at one of the meso-positions were synthesized by condensing appropriately functionalized unsymmetrical bithiophene diol and 16-telluratripyrrane in CH2 Cl2 under acid-catalyzed conditions. To demonstrate the reactivity of mono-functionalized telluradithiasapphyrins, we synthesized the first examples of covalently linked diphenyl ethyne bridged four novel 18π porphyrin/metalloporphrin-22π telluradithiasapphyrin dyads by coupling meso-ethynyl phenyl porphyrin with telluradithiasapphyrin containing meso-iodophenyl group under Pd(0) coupling conditions followed by metalation of porphyrin unit by treating free base dyad with appropriate metal salts. The dyads were characterized and studied by mass, 1D & 2D NMR, absorption, cyclic voltammetry, fluorescence and DFT techniques. The DFT analysis showed that the porphyrin/metalloporphyrin and sapphyrin units in dyads orient with each other in different angles and Zn(II) porphyrin-sapphyrin dyad (Zn-dyad) showed minimum whereas the free base dyad showed maximum angle of deviation. NMR, absorption, and redox studies indicated that the dyads exhibit the overlapping features of their constituted monomers and maintain their individual characteristic features. The steady-state fluorescence studies revealed that the fluorescence of the porphyrin/metalloporphyrin unit was significantly quenched due to possible energy/electron transfer from the porphyrin/metalloporphyrin unit to non-emissive sapphyrin unit in dyads.

Vacatadithiasapphyrins: Synthesis, Structure, and Spectral and Redox Properties.

Four examples of novel aromatic [22]vacatadithiasapphyrins were synthesized by refluxing appropriate [22]telluradithiasapphyrins in 1,2-dichlorobenzene in the presence of excess HCl followed by simple column chromatographic purification. The [22]vacatadithiasapphyrins can exist in three conformers "in", "out", and "zigzag" w.r.t the butadiene moiety, and under our experimental conditions, the "out" conformer was the major compound. The X-ray structure obtained for one of the "out" conformers of vacatadithiasapphyrins revealed that the macrocycle was planar similar to its parent telluradithiasapphyrin and showed effective π-delocalization over the entire macrocyclic core. NMR studies supported the formation of the "out" conformer and suggested that the vacatadithiasapphyrins were less aromatic than the parent telluradithiasapphyrins. Density functional theory, time-dependent DFT, and nuclear independent chemical shift studies indicated that the protonated form of vacatadithiasapphyrin was more aromatic than the parent protonated telluradithiasapphyrin. The absorption spectra of vacatadithiasapphyrins showed a typical strong Soret band at ∼488 nm and four relatively broad Q-bands in the region of 590-860 nm, and electrochemical studies suggest that vacatadithiasapphyrins were easier to oxidize and easier to reduce compared to the parent telluradithiasapphyrins.

Synthesis and Studies of Core-Modified Tellura Dithiasapphyrins.

Four different aromatic meso-substituted tellurophene-containing dithiasapphyrins were synthesized by acid-catalyzed [3+2] condensation of 16-telluratripyrrane with bithiophene diol in 22-23% yields. The structural, spectral, and electrochemical properties of tellura dithiasapphyrins were studied and compared with those of previously reported aza (pyrrole)- and other heterocycle (furan, thiophene, and selenophene)-containing dithiasapphyrins. Nuclear magnetic resonance studies indicated that the tellurophene ring in tellura dithiasapphyrins is in the normal conformation, facing toward the inner core, but flips in diprotonated derivatives to an inverted conformation, facing away from the macrocyclic core, unlike aza- and other heterocycle-containing dithiasapphyrins in which pyrrole and the corresponding heterocycle ring always prefer to be in inverted conformation in their neutral and protonated forms. The crystal structure obtained for one of the tellura dithiasapphyrins showed that the macrocycle is highly planar and the tellurophene ring is in the normal conformation. The absorption spectra of tellura dithiasapphyrins exhibited slight hypsochromic shifts compared to those of pyrrole- and other heterocycle-containing dithiasapphyrins. The redox studies indicated that the tellura dithiasapphyrins are electron deficient and readily undergoes reductions. Density functional theory and nuclear independent chemical shift studies indicated that the macrocycles are aromatic, and the computational results closely matched the experimental observations.

Tellurophene-Containing Core-Modified Pentaphyrin(2.1.1.1.1)s.

Various core-modified tellurophene-containing pentaphyrin(2.1.1.1.1)s were synthesized via (3 + 2) condensation of 16-telluratripyrrane with different heterodiols under mild acid catalyzed conditions in 5-12% yields. The formation of pentaphyrin (2.1.1.1.1) with a N2O2Te core was not successful due to its inherent instability. The new pentaphyrins were characterized and studied by HR-MS, 1D and 2D NMR, X-ray crystallography for one of the pentaphyrins, absorption and DFT/TD-DFT techniques. The NMR studies indicated their nonaromatic nature. The X-ray structure obtained for pentaphyrin(2.1.1.1.1) with N4Te core revealed that the macrocycle exists in a highly distorted nonplanar structure. The DFT studies showed that the macrocycles are nonaromatic and exists in highly distorted nonplanar geometry. Furthermore, as the core heterocyclic groups at ethene moiety were changed from pyrrole to furan to thiophene to benzene, the macrocycles tended toward more planar structures. The absorption spectra of pentaphyrins showed one strong sharp band in the region of 450-540 nm along with a broad band in the region of 700-800 nm. The pentaphyrin(2.1.1.1.1) with N4Te core upon protonation showed distinct color change in solution and large bathochromic shifts in absorption bands with an absorption in the NIR region.

Copper-Catalyzed Regioselective Synthesis of Multisubstituted Furans by Coupling between Ketones and Aromatic Olefins.

A regioselective synthesis of multisubstituted furan derivatives has been developed via Cu(II)-catalyzed intermolecular annulation of aryl ketones with a wide range of aromatic olefins under ambient air in good yields. This protocol is applicable to both cyclic and acyclic aryl ketones.

Rapid decadal evolution in the groundwater arsenic content of Kolkata, India and its correlation with the practices of her dwellers.

Increasing arsenic contamination in the groundwater is one of the biggest environmental challenges that the Bengal delta is facing today. Groundwater is still the main source of water for a large number of population in this region and therefore, significant presence of toxic arsenic has a direct consequence on human lives here. Moreover, arsenic also enters into the food chain through the consumed agricultural products grown in this area. Therefore, acquiring knowledge about the ever-changing map of arsenic contamination and employing adequate protective measures are of utmost importance. Here, we present a comprehensive municipal ward-wise map of the arsenic content of the shallow groundwater table of Kolkata-the most important and highly population dense city of the delta. Comparison with previously available data reveals a rapid change and the grim situation for the city. Our study suggests that it should be an immediate task of the administration to extend treated water service to the whole population of the city for direct consumption, and artificial recharge and maximum rainwater replenishment need to be taken up with utmost urgency to avoid intrusion of toxicity in biological food chains via agricultural products. We hope our study would drive the city planners to reconsider the existing urbanization and development plans of all the cities, placed over arsenic-contaminated groundwater aquifers.

Rhodium-Catalyzed Selective Mono- and Diamination of Arenes with Single Directing Site "On Water".

A Rh(III)-catalyzed selective C-H amination of 2-phenylpyridine derivatives is reported. With pyridine as a directing group, the reaction has high mono- or diamination selectivity, and a wide range of effective substrates, including electron-deficient and -rich aryl azides. Water helps to promote C-H activation, and the concept of a water promoted rollover mechanism is postulated for the diamination step. The reactions were conducted using a Schlenk flask and proceeded smoothly "on water" under atmospheric conditions with nitrogen gas as the only byproduct.

[RhCp*Cl2]2-catalyzed directed N-Boc amidation of arenes "on water".

Rhodium(III) catalysis "on water" is effective for directed C-H amidation of arenes. The catalytic process is promoted by OH groups present on the hydrophobic water surface and is inefficient in all (most) common organic solvents investigated so far. In the presence of easily prepared tert-butyl 2,4-dinitrophenoxycarbamate, a new and stable nitrene source, the "on water" reaction can efficiently provide the desired N-Boc-aminated products with good functional group tolerance.

Copper-mediated synthesis of substituted 2-aryl-N-benzylbenzimidazoles and 2-arylbenzoxazoles via C-H functionalization/C-N/C-O bond formation.

An efficient method for the transformation of N-benzyl bisarylhydrazones and bisaryloxime ethers to functionalized 2-aryl-N-benzylbenzimidazoles and 2-arylbenzoxazoles is described. The protocol involves a copper(II)-mediated cascade C-H functionalization/C-N/C-O bond formation under neutral conditions. Substrates having either electron-donating or -withdrawing substituents undergo the cyclization to afford the target heterocycles at moderate temperature.

Pd-catalyzed C-H activation/C-N bond formation: a new route to 1-aryl-1H-benzotriazoles.

A method for the C-H activation of aryl triazene compounds followed by intramolecular amination is described. It involves the use of a catalytic amount of Pd(OAc)(2) that efficiently effects the cyclization to provide 1-aryl-1H-benzotriazoles at moderate temperature.

Copper(II)-catalyzed conversion of bisaryloxime ethers to 2-arylbenzoxazoles via C-H functionalization/C-N/C-O bonds formation.

A copper(II)-catalyzed conversion of bisaryloxime ethers to 2-arylbenzoxazoles has been developed. The reaction involves a cascade C-H functionalization and C-N/C-O bond formation under oxygen atmosphere.

Cobalt-catalyzed intramolecular C-N and C-O cross-coupling reactions: synthesis of benzimidazoles and benzoxazoles.

Cobalt(ii)-complex catalyzes efficiently the intramolecular C-N and C-O cross-couplings of Z-N'-(2-halophenyl)-N-phenylamidines and N-(2-bromophenyl)benzamides to afford the corresponding substituted benzimidazoles and benzoxazoles in the presence of K(2)CO(3) at moderate temperature. The protocol is general, air stable and affords the products selectively in moderate to high yield.

Ligand-free copper-catalyzed synthesis of substituted benzimidazoles, 2-aminobenzimidazoles, 2-aminobenzothiazoles, and benzoxazoles.

The synthesis of substituted benzimidazoles, 2-aminobenzimidazoles, 2-aminobenzothiazoles, and benzoxazoles is described via intramolecular cyclization of o-bromoaryl derivatives using copper(II) oxide nanoparticles in DMSO under air. The procedure is experimentally simple, general, efficient, and free from addition of external chelating ligands. It is a heterogeneous process and the copper(II) oxide nanoparticles can be recovered and recycled without loss of activity.

Synthesis, structure, and application of self-assembled copper(II) aqua complex by H-bonding for acceleration of the nitroaldol reaction on water.

Simple addition: Copper(II) aqua complex 1 can be prepared in a one-pot synthesis and is self-assembled by H-bond interactions. Complex 1 is shown to accelerate the nitroaldol reaction on water, which is a heterogeneous process, requiring no additive or base, and 1 can be recycled without loss of activity. Copper(II) aqua complex 1 has been prepared in a one-pot synthesis. The single crystal X-ray analysis showed that the complex is self-assembled through aqua ligands by H-bond interactions and the copper(II) atoms are pentacoordinated with square pyramidal geometry. Complex 1 has been studied for the acceleration of the nitroalodol reaction on water. It is a clean technological process and the catalyst can be recycled without loss of activity.

A mild and regioselective method for alpha-bromination of beta-keto esters and 1,3-diketones using bromodimethylsulfonium bromide (BDMS).

Bromodimethylsulfonium bromide has been found to be an effective and regioselective reagent for alpha-monobromination of beta-keto esters and 1,3-diketones. A wide variety of beta-keto esters and 1,3-diketones undergo chemoselective alpha-monobromination with excellent yields at 0-5 degrees C or room temperature. The notable advantages of this protocol are no need of chromatographic separation, use of less hazardous reagent than molecular bromine, and no added base, Lewis acid, or other catalyst.