Chemistry in Confinement: Copper and Palladium Catalyzed Ecofriendly Organic Transformations within Porous Frameworks.

A concise account on the use of transition metals copper (Cu) and palladium (Pd), as their cations as well as nanoparticles exchanged/immobilized onto porous frameworks such as zeolites, metal organic frameworks (MOFs), covalent organic polymers (COPs) and hollow nanostructures, functioning as catalysts in organic synthesis is presented. This biomimetic account, "focusing on catalytic systems in confinement" within zero-dimensional microenvironments and second sphere coordination covers primarily results from our group on N-sulfonylketenimine mediated cycloaddition, hydrogenation and C-C bond forming reactions, thus providing an interesting insight into the versatility and utility of these Cu and Pd catalysts. Other significant advantages and green credentials of confinement such as stability, selectivity, reusability, promotion of multicomponent reactions, use of green solvents, atom economy, and use of ambient conditions are highlighted at appropriate places. In the final section, our views on the current achievements and the future prospects in this area are summarized.

Copper(i)-Y zeolite catalyzed N-sulfonylketenimine mediated annulation of hydroxynaphthoquinones: syntheses of naphtho[2,1-b]furan-2,5-diones and benzo[de]chromene-2,6-diones.

An efficient one pot synthesis for the construction of novel naphtho[2,1-b]furan-2,5-diones and benzo[de]chromene-2,6-diones using copper(i)-Y zeolite catalyzed reaction of N-sulfonylketenimine with 2-hydroxy-1,4-naphthoquinone and 5-hydroxy-1,4-naphthoquinone followed by the elimination of p-toluenesulfonamide is reported. The intermediate N-sulfonylketenimine, generated by (3+2) cycloaddition/ring-opening reaction/retro-Wolff rearrangement, cascade, and annulation, promotes the reaction involving the inter- and intramolecular nucleophilic addition/dehydration followed by hydrolysis and elimination of p-toluenesulfonamide to afford the target products in good yield.

Chemical constituents from the flowering buds of Bauhinia tomentosa Linn (FBBT).

Isolation and characterisation of compounds, 1-(2'-hydroxy-4'-methoxyphenyl)-3-(4″-methoxyphenyl)-2-hydroxypropane-1,3-dione (1), 5-hydroxyflavone (2), 3,5,7,3',4'-pentahydroxyflavone (3), 3,5,7,2',4'-pentahydroxyflavone (4) and 5,7,3',4'-tetrahydroxyflavone-3-O-rhamnoside (5) are reported from the air dried flowering buds of Bauhinia tomentosa Linn. Their structures are determined on the basis of extensive chemical and spectral evidences. Compound (1) is reported for the first time from the plant source. While compounds (2) and (4) are reported for the first time from this genus, compound (2) is reported for the second time from the natural source.

Fabrication of Pd Nanoparticles Embedded C@Fe3O4 Core-Shell Hybrid Nanospheres: An Efficient Catalyst for Cyanation in Aryl Halides.

Isolated chemical reactors were fabricated by integrating catalytically active sites (Pd) with magnetic functionality (Fe3O4) along with carbon while preserving the constituents functional properties to realize the structure-property relationship of Pd by comparing the catalytic activity of spherical Pd NPs with cubical Pd NPs for cyanation in aryl halides using K4[Fe(CN)6] as a green cyanating agent to yield corresponding nitriles. The superior catalytic reactivity of the cubical Pd NPs is attributed to the larger number of {100} surface facets. The TEM images of reused catalyst shows the change in structure from cubical to spherical nanoparticles, attributed to the efficient leaching susceptibility of Pd {100} surface facets. The cubical Pd NPs on carbon@Fe3O4 is attractive in view of its high catalytic efficiency, easy synthesis, magnetic separability, environmental friendliness, high stability, gram scale applicability, and reusability.

Copper(I)-Y Zeolite-Catalyzed Regio- and Stereoselective [2 + 2 + 2] Cyclotrimerization Cascade: An Atom- and Step-Economical Synthesis of Pyrimido[1,6-a]quinoline.

An elegant copper(I)-Y zeolite-catalyzed tandem process, involving ketenimine-based termolecular [2 + 2 + 2]/[NC + CC + NC] cycloaddition, using sulfonyl azide, alkyne, and quinoline, to prepare pyrimido[1,6-a]quinolines is reported. In this straightforward, highly atom- and step-economical protocol, copper(I) promotes for azide-alkyne [3 + 2] cycloaddition which is followed by ring-rearrangement/ketenimine formation/regio- and stereoselective [2 + 2 + 2] termolecular cycloaddition and dehydrogenation cascade to yield selectively the E-isomer of pyrimido[1,6-a]quinoline.

A New Isoflavone Apioglucoside from the Roots of Dalbergia spinosa.

Targeting the discovery of novel natural products, the roots of Dalbergia spinosa Roxb has yielded a new isoflavone apioglycoside, 5-hydroxy-6-methoxy- 3',4'-methylenedioxy-7-[(6-O-ß-D-apiofuranosyl-ß-D-glucopyranosyl) oxy]isoflavone (dalspinin-7-O-ß-D-[apiofuranosy (1-->6)] glucopyranoside) (1), together with the known isoflavones, dalspinin (2), dalspinosin (3) and caviunin (4). Their structures were elucidated on the basis of extensive spectral and chemical evidence. To the best of our knowledge, this is the first report of the occurrence of an apioglucoside of dalspinin in Nature.

Triazine-based mesoporous covalent imine polymers as solid supports for copper-mediated Chan-Lam cross-coupling N-arylation reactions.

The synthesis of a novel mesoporous covalent imine polymeric (MCIPs) material, involving simple Schiff-base chemistry, is reported. This highly functionalised nitrogen-rich material acts as a good support for immobilising Cu(II) ions, exhibiting excellent catalytic activity in promoting the Chan-Lam cross-coupling reaction between biologically active amines and arylboronic acids. The performance of this catalyst is also evident from its broad substrate scope, high stability, real heterogeneity, mild reaction conditions and reusability without loss of activity. The observed results will provide additional scope on the design and catalytic applications of this emerging class of materials.

Highly selective "turn-on" fluorescent and colorimetric sensing of fluoride ion using 2-(2-hydroxyphenyl)-2,3-dihydroquinolin-4(1H)-one based on excited-state proton transfer.

A simple, highly selective and sensitive colorimetric system for the detection of fluoride ion in an aqueous medium has been developed using 2-(2-hydroxyphenyl)-2,3-dihydroquinolin-4(1H)-one. This system allows selective "turn-on" fluorescence detection of fluoride ion, which is found to be dependent upon guest basicity. An excited-state proton transfer is proposed to be the signaling mechanism, which is rationalized by DFT and TD-DFT calculations. The present sensor can also be applied to detect fluoride levels in real water samples.

The aminocyclodextrin/Pd(OAc)2 complex as an efficient catalyst for the Mizoroki-Heck cross-coupling reaction.

An aminocyclodextrin/Pd(OAc)2 complex is used as an efficient, reusable catalyst in the Mizoroki-Heck reaction of aryl halides/triflates with olefins to give carbon-carbon-coupled products in good to excellent yields. This simple, efficient catalytic system is applicable to a wide range of aryl and heteroaryl halides/triflates and olefins. This environmentally benign procedure is less hazardous, milder, uses a catalytic amount of ligand and Pd(OAc)2 , avoids an inert atmosphere, and catalyst recovery and reusability are achieved.

Per-6-amino-ß-cyclodextrin as a chiral base catalyst promoting one-pot asymmetric synthesis of 2-aryl-2,3-dihydro-4-quinolones.

A highly efficient one-pot synthesis of enantiomerically enriched 2-aryl-2,3-dihydroquinolin-4(1H)-ones has been carried out for the first time using per-6-ABCD as a supramolecular host, chiral base catalyst, and a reusable promoter to give the corresponding scaffold with high yield (up to 99%) and enantiomeric excess (up to 99%). The catalyst is recovered and reused without loss in its activity.

A highly selective ratiometric fluorescent chemosensor for Cu(ii) based on dansyl-functionalized thiol stabilized silver nanoparticles.

A fluorescent chemosensor for Cu2+ ions based on dansyl-functionalized thiol stabilized silver nanoparticles containing 2-aminothiophenyl units as the Cu2+ binding sites is developed. A decrease in fluorescence at 497 nm and an increase in fluorescence at 410 nm with an isoemissive point at 445 nm upon the addition of Cu2+ ions is attributed to the formation of a Cu2+ complex in aqueous acetonitrile based on an energy transfer mechanism. This sensor has excellent sensitivity and selectivity over other metal ions and has a detection limit as low as 5.0 × 10-10 mol L-1.

An acyclic, dansyl based colorimetric and fluorescent chemosensor for Hg(II) via twisted intramolecular charge transfer (TICT).

An efficient fluorescent chemosensor for Hg(2+) ion, based on 5-(dimethylamino)-N-(2-mercaptophenyl)naphthalene-1-sulfonamide, has been developed. It exhibits Hg(2+)-selective on-off fluorescence quenching behavior via twisted intramolecular charge transfer (TICT) mechanism, which is rationalized by time dependent density functional theory (TD-DFT) calculations. The system exhibits visible color change from colorless to gray upon Hg(2+) binding with very high selectivity and sensitivity (as low as 5.0×10(-10)molL(-1)) over other metal ions such as K(+), Na(+), Ag(+), Mn(2+), Ca(2+), Ba(2+), Fe(2+), Zn(2+), Pb(2+), Cu(2+), Sn(2+), Cd(2+), Ni(2+) and Co(2+). The present sensing system is also successfully applied for the detection of Hg(2+) ion in real samples.

An intramolecular charge transfer (ICT) based chemosensor for silver ion using 4-methoxy-N-((thiophen-2-yl)methyl)benzenamine.

4-Methoxy-N-((thiophen-2-yl)methyl)benzenamine was found to be a highly selective chemosensor for Ag(+) ion in methanol-water (1 : 1 v/v) mixture over other metal ions such as Na(+), K(+), Li(+), Cu(+), Ba(2+), Cd(2+), Co(2+), Cu(2+), Fe(2+), Hg(2+), Mn(2+), Ni(2+), Pb(2+) and Zn(2+) with a limit of detection (LOD) is 5.0 × 10(-6) mol L(-1). Upon binding to Ag(+) ion, a strong fluorescent enhancement is observed which is attributed to an increase in intramolecular charge transfer (ICT). The proposed mechanism is strongly supported by TD-DFT calculations.

Highly selective fluorescent sensing of fenitrothion using per-6-amino-ß-cyclodextrin:Eu(III) complex.

A unique, efficient, highly sensitive and selective fluorescent chemosensor for fenitrothion has been reported for the first time using per-6-amino-ß-cyclodextrin:Eu(III) complex. Among the various pesticides, the sensitivity response is found to be in the order, fenitrothion>>>quinalphos>methylparathion>parathion>methylparaoxon>paraoxon>fenchlorphos>profenofos>malathion. A detection limit as low as 1 × 10(-12)M for fenitrothion sensing is realized with a 2.4% relative standard deviation (RSD) of three consecutive runs. The per-6-amino-ß-cyclodextrin:Eu(III):pesticide complexes and their sensing mechanism are evidenced from emission, NMR, FT-IR, binding constant measurement, Job's plot, ICD spectra, ESI-MS, lifetime measurements and molecular modeling studies. The proposed sensing is a consequence of Absorption Energy Transfer Emission (AETE) process as a result of better encapsulation of fenitrothion inside the cavity of per-6-amino-ß-cyclodextrin:Eu(III) complex. The remarkable sensitivity and selectivity of fenitrothion compared to other OPs, is attributed to a more deeper binding and tighter fit of fenitrothion inside the CD cavity, which is evident from binding constant values and molecular modeling studies. This tighter fit ensures the replacement of two coordinating water molecules on Eu(III) ion, which may have contributed to the more selective sensing of fenitrothion.

Cascade synthesis of bis-N-sulfonylcyclobutenes via Cu(I)/Lewis acid-catalyzed (3 + 2)/(2 + 2) cycloadditions: observation of aggregation-induced emission enhancement from restricted C=N photoisomerization.

A remarkable role of Lewis acid additives in syntheses of bis-N-sulfonylcyclobutenes via copper(I) catalyzed (3 + 2)/(2 + 2) cycloaddition cascade of sulfonyl azides and terminal alkynes is described. In addition, these cyclobutenes display a unique aggregation-induced emission enhancement (AIEE), reported for the first time, arising predominantly from restricted rotation in C=N photoisomerization in the solid state.

Isoxazoles incorporated N-substituted decahydroquinolines: a precursor to the next generation antimicrobial drug.

We report here a simple entry into N-substituted decahydroisoxazoloquinoline system with substituents at position 3 and 4 from the readily available substrates for the first time. The synthesized isoxazoloquinolines were evaluated against six bacterial and four fungal strains. The results suggest that the decahydroisoxazolo[4,3-c]quinoline scaffold has the potential to be developed into therapeutically useful antimicrobial agents.

Design and synthesis of 3,5-diarylpiperidin-2,6-diones as anticonvulsant agents.

The present Letter describes a one-pot multi-component method that allows the efficient and mild preparation of 3,5-diphenylpiperidin-2,6-dione and a new series of 3,5-diarylpiperidin-2,6-dione derivatives from ethyl 2-arylacetates, formaldehyde and ammonia/aliphatic/aromatic amines. The structures of the compounds were elucidated by IR, NMR spectroscopic data and microanalyses. The anticonvulsant activities of these compounds were evaluated by maximal electroshock seizure test and were also evaluated for motor impairment. Among the synthesized compounds, 5a, 5b, 5d, and 5e could be considered potentially the most useful and safe therapeutic compound and 5g, 5i, 5j, 5m, and 5o exhibit potent activities.

Autofluorescence in BrdU-positive cells and augmentation of regeneration kinetics by riboflavin.

The earthworm, Eudrilus eugeniae, has a prodigious ability to regenerate lost segments. The skin of the worm has an outermost epidermal layer followed by a thick circular muscle layer and an innermost thin longitudinal cell layer. During the process of regeneration, the circular muscle layer decreased in thickness, and longitudinal cell layer increased. The histological analysis of the regenerated worm shows that the longitudinal cell layer forms the regeneration blastema. BrdU-labeling retention assay confirmed that the circular muscle and longitudinal cell layers have BrdU-positive cells, which migrate from the adjacent segments to the regeneration blastema. In addition, it was noted that the cells of the earthworm, E. eugeniae, have the property of autofluorescence. Autofluorescence was found in the cytoplasm, but not in the nucleus. It has been also found that the major source for autofluorescence is riboflavin. Further, it was also demonstrated that supplementation with riboflavin increases the rate of regeneration, while regeneration was hampered by reduced levels of riboflavin. The importance of riboflavin in regeneration was also confirmed by rescue assay. In addition, it was also identified that BrdU-positive cells are highly fluorescent compared to the surrounding cells.

Copper(I)-catalyzed three component reaction of sulfonyl azide, alkyne, and nitrone cycloaddition/rearrangement cascades: a novel one-step synthesis of imidazolidin-4-ones.

A novel one-pot azide-alkyne/ketenimine-nitrone cycloaddition sequence that is induced by copper(I) and allows the transformation of sulfonyl azides, alkynes, and nitrones to highly substituted imidazolidin-4-ones is described. The corresponding heterogeneous version utilizing Cu(I)-modified zeolites as recyclable heterogeneous catalysts shows marginally improved yield and diastereoselectivity.

Syntheses of 5-substituted 1H-tetrazoles catalyzed by reusable CoY zeolite.

A simple and efficient route for the synthesis of 5-substituted 1H-tetrazoles catalyzed by CoY zeolite is reported. The salient features of this atom-economical, cost-effective, and high-yield cobalt-catalyzed protocol are aerobic conditions, lower reaction time, and milder reaction conditions without additives. Other advantages include experimental ease of manipulation, safer alternative to hazardous, corrosive, and polluting conventional Lewis acid catalysts, recovery, and reusability with consistent catalytic activity. The results are rationalized by proposing a suitable mechanism.