“On Water” Sustainable Synthesis of 1,5-Disubstituted Tetrazoles via Ugi-Azide Reaction through Perturbation of Kosmotropes Using Nacl

A Novel and Efficient Nano Alumina Based Cu (II) Catalyst for Three- Component Synthesis of 5-Substituted-1H-Tetrazoles

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Tetrazoles as one of the most important synthetic heterocyclic compounds have so many applications in organic chemistry, the photographic industry, coordination chemistry, explosives and in particular, medicinal chemistry. Numerous methods have been reported in the literature for synthesis of tetrazoles, but much of them have some drawbacks including the use of strong Lewis acids or expensive and toxic metals and employment of acidic media. Azides may react with acids to yield toxic and flammable HN3 gas. Furthermore, many methods used high polar solvents such as DMF at high temperatures and very tedious work-up. Heterogeneous catalysts are preferred because of owing to easy handling, safety, recoverability and reusability. Catalyst separation and recycling is highly desirable because catalysts are often very expensive. On the other hand, in spite of higher reactivity and selectivity of homogeneous catalysts, the difficulty of separating them from the reaction medium can lead to the problem of reusing the catalyst. Also, most homogeneous catalysts are thermally unstable. To benefit advantages of both types of catalysts, one solution is using nanoparticles. Their higher surface area is the advantages of nanoparticles, which allows them to enhance the reaction rate. Many commercially important catalysts include active nanoparticles spread on high area oxide supports. Such catalysts are highly complex materials that are optimized to work for plenty of turnovers at high reaction rates and with high selectivity. Aldehyde (1 mmol), hydroxylamine hydrochloride (0.10 mg, 1.5 mmol), sodium azide (0.10 g, 1.5 mmol), distilled water (5 mL) and nano Al2O3@PCH-Cu (II) (0.01g, 1.04% mol) were added to round bottom flask (25 mL) and stirred at room temperature. After the completion of the reaction, water (10 mL) was added into reaction mixture and filtered. Excess sodium azide and hydroxylamine hydrochloride are dissolved in water and the catalyst remains on the filter. Extraction of product with diethyl ether (3×10 mL) and then evaporation of ether afforded the product. The product was recrystallized using hot ethanol to obtain pure product. We synthesized a novel, stable, highly reactive and efficient nano-sized heterogeneous catalyst (nano Al2O3@PCH-Cu (II)). We characterized it by FT-IR, ICP, SEM, TGA and EDX analysis. This catalyst was used for the efficient one-pot three-component synthesis of 5-substituted-1H-tetrazoles. An one-pot three-component synthesis of 5-substituted-1Htetrazoles is conducted, a reaction between various benzaldehydes, hydroxyl amine hydrochloride and sodium azide in the presence of a novel and highly efficient nano alumina supported poly(carboxylic acid hydrazide) Cu(II) complex, nano Al2O3@PCH-Cu(II), as heterogeneous catalyst in H2O at room temperature. This method has very mild reaction conditions as well as the advantages of easy separation and reusability of the catalyst, very short reaction times, high yields and using H2O as green solvent. Furthermore, using this method very high TON and TOF values obtained for all isolated products.

Site-specific role of bifunctional graphitic carbon nitride catalyst for the sustainable synthesis of 3,3-spirocyclic oxindoles in aqueous media

Functionalized graphitic carbon nitride (Sg-C₃N₄) has been manufactured and used as a reusable catalyst for the one-pot production of various spiro-pyrano chromenes and spiro indole-3,1′-naphthalene tetracyclic systems in aqueous media. An ultrasound-assisted method has been used for the functionalization of g-C₃N₄. The catalytic functionalities and the structural integrity of the catalyst were characterized via different analytical tools. The catalytic site-specific role of Sg-C₃N₄ was confirmed via various control experiments in one-pot reaction sequences. We recognized that Sg-C₃N₄ acts as a bifunctional acid–base catalyst for the first reaction sequence whereas it is an acidic catalyst for the second reaction sequence during the one-pot production of various spiro-pyrano chromenes. In addition, the bifunctional acid–base catalytic role of Sg-C₃N₄ has been confirmed for the first reaction sequence whereas it has a basic catalytic role for the second reaction sequence during the one-pot production of spiro indole-3,1′-naphthalene tetracyclic systems. Diverse C–C, C–O, and C–N bonds, six-membered cycles, stereogenic centers, and spiro frameworks were formed in a single reaction, enhancing the biocidal profile and possibly resulting in the discovery of new medicinal properties. The mild reaction environment, simple workup, easy separation, low cost, heterogeneity, and recyclability of Sg-C₃N₄ are some rewards of this approach.

Functionalized graphitic carbon nitride (Sg-C₃N₄) has been manufactured and used as a reusable catalyst for the one-pot production of various spiro-pyrano chromenes and spiro indole-3,1′-naphthalene tetracyclic systems in aqueous media.

The graphite-catalyzed ipso-functionalization of arylboronic acids in an aqueous medium: metal-free access to phenols, anilines, nitroarenes, and haloarenes

An efficient, metal-free, and sustainable strategy has been described for the ipso-functionalization of phenylboronic acids using air as an oxidant in an aqueous medium. A range of carbon materials has been tested as carbocatalysts. To our surprise, graphite was found to be the best catalyst in terms of the turnover frequency. A broad range of valuable substituted aromatic compounds, i.e., phenols, anilines, nitroarenes, and haloarenes, has been prepared via the functionalization of the C-B bond into C-N, C-O, and many other C-X bonds. The vital role of the aromatic π-conjugation system of graphite in this protocol has been established and was observed via numerous analytic techniques. The heterogeneous nature of graphite facilitates the high recyclability of the carbocatalyst. This effective and easy system provides a multipurpose approach for the production of valuable substituted aromatic compounds without using any metals, ligands, bases, or harsh oxidants.

Regioselective condensation of hydroxyaromatic compounds with 2,5-dimethoxytetrahydrofuran: facile one-pot synthesis of new substituted diaryl-fused 2,8-dioxabicyclo[3.3.2]nonanes comprising central ketal moieties

Regioselective synthesis of a series of novel diaryl- and naphthyl-fused 2,8-dioxabicyclo[3.3.2]nonanes was accomplished by a one-pot reaction of p-substituted phenols and 2-naphthol with 2,5-dimethoxytetrahydrofuran.

Chemical Waltz of Organic Molecules "On Water": Saline-Assisted Sustainable Regioselective Synthesis of Fluorogenic Heterobioconjugates via Click Reaction

A new sustainable green protocol for obtaining highly fluorogenic heterobioconjugates by a well-known copper-mediated azide-alkyne cycloaddition click reaction of nonfluorescent 3-azidocoumarins/benzyl azides (2a-f) and terminal alkynes (1a-e) using aqueous NaCl as a cheap and nontoxic salting-out agent under ultrasonication at ambient temperature is described. The presence of aqueous NaCl significantly influences the reaction by disturbing the water kosmotropes and augments the hydrophobic interaction of water-insoluble reactants, thus making the reaction feasible in water at neutral pH. The "beauty" of the presented ecofriendly approach is further boosted up by recycling the aqueous filtrate of the reaction mixture without further addition of NaCl, CuSO₄·5H₂O, and Na ascorbate up to seven cycles, resulting in effectively low copper loading (100 ppm) with excellent turn-over number (4850) and turn-over frequency (88.18 min^-1). A gram-scale synthesis was also successfully achieved with 92% yield, further elaborating the scope of this methodology.