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Relevant academic research and scientific papers

Aldazines in the Castagnoli-Cushman Reaction

Aldazines were employed in the Castagnoli-Cushman reaction of homophthalic anhydride for the first time. The reaction proved to be distinctly diastereoselective when conducted at room temperature in acetonitrile, yielding predominantly the kinetic cis -co

Selective Reduction of Azines to Benzyl Hydrazones with Sodium Borohydride Catalyzed by Mesoporous Silica-Supported Silver Nanoparticles: A Catalytic Route towards Pyrazole Synthesis

The catalytic activity of supported silver nanoparticles on mesoporous silica was studied, for the selective reduction of azines into benzyl hydrazones using sodium borohydride as mild reducing agent. Different sizes of silver nanoparticles supported on mesoporous silica (Ag/HMS) were successfully prepared by two methods, i.e., wet impregnation followed by reduction with hydrogen at 350 °C and in situ deposition/reduction with a mixture of amines (ethanolamine and ethylenediamine). The Ag/HMS (amines) catalyst was found to promote the selective 1,2-reduction of aryl-substituted azines, compared to the corresponding 1,4-reduction that occurs in general reduction processes. This catalytic transfer hydrogenation process found to be clean, fast and quantitative (>99% yields and selectivity) towards benzyl hydrazone synthesis under mild conditions. Of great importance is that under the present catalytic conditions reducible functional groups remain intact. Formal kinetics, support the in situ formation of silver hydride species being responsible for the reduction process. The presence of protic polar methanol enhanced the catalytic activity of Ag/HMS. Based on the recycling studies the catalytic system Ag/HMS-NaBH4 was found to catalyze the selective reduction of azines nine times without significant loss of its activity. Finally, a one-pot reaction between the in situ produced benzyl hydrazones and a series of nitrostyrenes readily provided the regioselective synthesis of 1,3,5-subtituted pyrazoles, highlighting a useful synthetic application of the catalytic protocol. (Figure presented.).

Solvent-free, [Et3NH][HSO4] catalyzed facile synthesis of hydrazone derivatives

In the present study, a library of hydrazone analogues 2(a-j) and 4(a-e) were synthesized, which were typically accessed via a solvent-free facile nucleophilic addition between hydrazine hydrate and appropriately substituted aromatic aldehydes 1(a-j) and 3-formylchromones 3(a-e). The molecular structure of compound (2f) was well supported by single crystal X-ray crystallographic analysis and also verified by DFT calculations. This new synthetic, eco-friendly, sustainable protocol resulted in a remarkable improvement in the synthetic efficiency (90-98% yield), high purity, using [Et3NH][HSO4] as a catalyst and an environmentally benign solvent eliminating the need for a volatile organic solvent and additional catalyst. This ionic liquid is air and water stable and easy to prepare from cheap amine and acid. The present methodology is a green protocol offering several advantages such as, excellent yield of products, minimizing production of chemical wastes, shorter reaction profile, mild reaction conditions, simple operational procedure, easy preparation of catalyst and its recyclability up to five cycles without any appreciable loss in catalytic activity. The optimization conditions carried out in the present study revealed that 20 mol% of ionic liquid catalyst under solvent-free condition at 120°C are the best conditions for the synthesis of hydrazone derivatives in excellent yields.

Rapid, chemoselective and facile synthesis of azines by hydrazine/I2

We report the reaction of hydrazine hydrate with carbonyl compounds in the presence of molecular iodine at 0-10°C, which affords symmetrical azines in excellent yields in 1 to 4 min without any adverse effect on other substituents. The reactions are rapid and chemoselective, afford excellent yields, and have high-purity products. The workup procedure is environmentally benign and does not require solvent extraction. Copyright Taylor & Francis Group, LLC.

Selective protection of carbonyl compounds as azines and their facile regeneration

Carbonyl compounds with freshly prepared hydrazinium formate successfully yielded the corresponding azines in excellent yields. In turn, azines were deprotected to the corresponding carbonyls using triethylammonium chlorochromate chemoselectively. Copyright Taylor & Francis Group, LLC.

Synthesis of bishydrazones (aldazines)

Bishydrazones have been prepared by thermolysis of aldehyde hydrazone under reduced pressure in a sealed tube at 120-30°C. The possible mass spectral fragementation mode of bishydrazones have also been discussed.