Current Organocatalysis - Volume 6, Issue 1, 2019

Architectural photocatalysts have considered to be an eco-friendly and green technology for protection and remediation of environment and the emergence of these photocatalysts also provides a new way for solar energy conversion and utilization as it only works under sunlight irradiation. Based on latest research from related group and other colleagues, this paper mainly reviews the different synthesis of architectural photocatalysts and its working mechanism and introduces some relevant applications, such as the degradation of organic pollutants, the photocatalytic hydrogen production and CO2 reduction and so on. What's more, the opportunities and challenges encountered in the area of architectural photocatalysts and their potential applications in more fields have been briefly illustrated.

Background: The conception of ‘Green chemistry’ is the much inventive chemistry which is potent and more environmentally benign. It is notable that many organic reactions take place in conventional organic solvents, known as volatile organic compounds. Being concerned about the environmental impact, we report a promoting medium, coconut juice (ACC) for one-pot synthesis of biscoumarins and pyranocoumarins which is safe, harmless, green and environmentally benign. Methods and Results: Substituted biscoumarins have been achieved by the reaction of biscoumarin and substituted aromatic aldehydes in presence of ACC which acts as a green catalyst cum solvent. Each reaction showed good to excellent yield in presence of both electron donating as well as electron withdrawing group on aromatic aldehyde without formation of any by-products. Similarly, pyranocoumarins have been achieved by the reaction of biscoumarin, substituted aromatic aldehydes, active methylene nitrile in presence of ACC. All the reactions proceed smoothly and gave higher yields in case of malononitrile in comparison of ethyl-2-cyanoacetate. Conclusion: A simple, eco-friendly and novel procedure was demonstrated for the synthesis of biscoumarins and pyranocoumarins using natural feedstock coconut juice. The major importance of using ACC juice is higher yields, no work-up and no column chromatography.

Background: 4-Arylmethylideneisoxazol-5(4H)-ones are a class of organic compounds with a variety of applications in the agriculture, filter dyes, photonic devices, and pharmaceutical industries. They are also used as synthetic precursors for the synthesis of other organic compounds. As a result, efforts are being made to search new and available catalyst and green methods toward their synthesis. Objective: The aim of this work is to investigate the catalytic activity of salicylic acid as an inexpensive, easy to handle, and safe catalyst to synthesis of some derivatives of isoxazole-5(4H)-ones in water medium. Methods: To aqueous solution of equal amounts of aryl/heteroaryl aldehydes, β-ketoesters, and hydroxylamine hydrochloride; salicylic acid (15 mol%) was added and the reaction mixture was stirred at room temperature for a specified periods. The precipitated product was filtered and washed with water to obtain 3-substituted-4-arylmethylideneisoxazol-5(4H)-ones. The reaction conditions were also optimized and extended to synthesis other isoxazol-5(4H)-ones. Results: The salicylic acid is found to possess acceptable catalytic activity for the promotion of three-component cyclocondensation of aryl/heteroaryl aldehydes, β-ketoesters, and hydroxylamine hydrochloride. The three-component reaction led to construction of 3-substituted-4-arylmethylideneisoxazol- 5(4H)-ones in good to high isolated reaction yields. Conclusion: The efficient and environmental friendliness procedure for the synthesis of isoxazol- 5(4H)-ones is introduced. The reaction also carried out smoothly in water as a cost-effective, simple, green, and non-toxic solvent at room temperature without using heating, microwave, and ultrasound sources.

Background: The AFM-techniques have been used for the research of the role of intermolecular H-bonds and stable supramolecular nanostructures, based on effective catalysts of oxidation processes, which are also models of Ni(Fe)ARD Dioxygenases, in mechanisms of catalysis. Methods and Results: The role of Histidine and Tyrosine ligands in the mechanisms of catalysis by FeARD on model systems is discussed based on AFM and UV-Spectroscopy data. Conclusion: We first offer the new approach – method of atomic force microscopy (AFM) – to study the possibility of the formation of supramolecular nanostructures, and also for assessing of role the intermolecular hydrogen bonds (and the other intermolecular non-covalent interactions) in mechanisms of homogeneous and enzymatic catalysis with nickel and iron complexes.

Background: We are submitting an easy, effective and environmentally benign protocol for the synthesis of 18 different 1,2-dihydroquinazoline derivatives. Methods: We implemented [TMA][OH] ionic liquid mediated hydrotalcite clay catalytic system as a green catalyst to perform this reaction. Results: Three-component reaction pathway was utilized to synthesize 1,2-dihydroquinazoline derivatives using aromatic aldehydes, 2-amino benzophenones, and ammonium acetate with green and recyclable ionic liquid mediated hydrotalcite clay catalytic system. Conclusion: The notable highlights of this method comprise short reaction time, operational simplicity, high yields, and high selectivity. Additionally, the catalyst can be recovered and recycled for up to eight cycles without any loss in catalytic activity.

Background: ADA as N-(2-Acetemido) iminodiacetic acid has been widely used in preparation of organic buffers and protein-free media for fibroblasts as chelating agent chicken embryo fibroblasts as tridentate chelating agent ligand. However, a little attention has been focused to the behavior of its oxidation in aqueous acidic solutions. Accordingly, a lack of information on the aqueous chemistry of oxidation of ADA in acidic solutions was recognized. Therefore, we have prompted to undertake the present work with the aims at shedding more light on the behavior of oxidation and the nature of oxidation products. Again, it aims to compensate the lack of information about the aqueous chemistry of ADA and the nature of electron-transfer for redox reactions involving permanganate ion as a multi-equivalent oxidant. Method: A spectrophotometric investigation of oxidation of ADA by permanganate ion in aqueous perchlorate solutions has been investigated. Results: Absorbance-time curves indicated the presence of two distinct stages for the oxidation process. The experimental results indicated a decrease in the reaction rates with increasing the [H+], ionic strength and F- ions. Again, the reaction rates were found to increase with increasing the added Mn2+ and temperature. Conclusion: These results indicated that the oxidation process was of acid-inhibition nature and proceeding by free-radical intervention mechanism. Again, the reactive species in the fast second stage was the Mn4+ species formed in the initial stage. The activation parameters have been evaluated from the temperature dependence of the rate constants. A tentative reaction mechanism was suggested for such redox reaction.

Background: This research introduces an effective and green method for the synthesis of polysubstituted 2-pyrrolidinone derivatives as biologically-active heterocyclic compounds using multi- component reactions using Fe3O4@L-arginine as a reusable organocatalyst. Material and Method: The Fe3O4@L-arginine nanoparticles were prepared by a facile one-step approach and the structure elucidation of the magnetic nanocatalyst has been done using various spectroscopy techniques. Results: L-arginine-functionalized magnetite nanoparticles were obtained with particle sizes around 10 nm. Fe3O4@L-arginine exhibited strong catalytic activity to obtain some polysubstituted 2- pyrrolidinone. Conclusion: The considerable advantages of this research are short reaction times, excellent yields, simple workup procedure and reusability of the nanocatalyst which is in good agreement with green chemistry disciplines. The study on the reusability of the Fe3O4@L-arginine nanoparticles showed that the recovered catalyst could be reused six consecutive times.

Background: A green, recyclable and reusable chitosan catalyst has been utilized for the synthesis of 5-amino-2,3-dihydrobenzo[d]thiazole-4,6-dicarbonitrile and its derivatives. Methods and Results: Three-component reaction protocol incorporates the reaction of aldehydes, malononitrile and rhodanine derivatives. This is examined as an efficient route for the synthesis of dicarbonitriles utilizing a green, biodegradable, environmentally benign, and easily available chitosan catalyst. In the reported protocol, catalyst can be recycled and not any substantial dropping in its catalytic activity during the recycling steps was obtained. Conclusion: A green and environmentally benign, one pot three-component protocol has been illustrated for the synthesis of 5-amino-2,3-dihydrobenzo[d]thiazole-4,6-dicarbonitrile derivatives. Adequately yield products were gained via the natural catalytic approach with the recyclability of the catalyst. The use of chitosan represents this procedure as an attractive substitute for the synthesis of biaryls complex by multicomponent reaction condition.