Current Catalysis - Volume 7, Issue 1, 2018

Background: Due to significant biological activity associated with N-, O- and Sheterocycles, a number of reports for their synthesis have appeared in recent decades. Traditional approaches require expensive or highly specialized equipment or would be of limited use to the synthetic organic chemist due to their highly inconvenient approaches. This review summarizes the applications of platinum metal with emphasis of their synthetic applications for heterocylces. In summary, this review article describes the synthesis of different sized heterocyclic rings containing different heteroatoms. Objective: The key area of research these days is the development of rapid, efficient and versatile tools for the construction of heterocycles and much prominence was gained by protocols that involved transition- metal catalysis. The traditional strategies that involved long reaction times, harsh conditions and limited substrate scopes are overshadowed by these catalytic practices. Conclusion: The efficient and chemoselective synthesis of heterocycles by this technique has appeared as an important tool. This review shows a highly dynamic research field and the employment of platinum catalysts in organic synthesis. Several strategies have been pointed out in the past few years, to meet more sustainable, efficient and environmentally benign chemical products and procedures. The catalytic strategies have been the focus of intense research because they avoid the use of toxic reagents. Among these catalytic strategies, highly rewarding and an important method in heterocycles synthesis is metal catalyzed synthesis.

Background: Polyoxometalates are an ever more essential class of environmentally benign catalysts. Among them, Keggin heteropolyacids have been highlighted because they are catalysts with attractive redox and acid properties, which may be easily tunable through structural changes. In particular, the total or partial exchanges of their protons by large cations make heteropolyacid insoluble salts with high surface area, potentially useful in a plethora of acid or redox catalyzed reactions. The purpose of this mini review is to highlight some recent advances achieved in the total or partially exchanged heteropolyacid salt-catalyzed routes for the production of chemicals and fuels. Methods: We undertook a structured search of papers that were published in high-impact journals, which confirm the quality of retrieved papers. The main characteristics of screened papers were described, with emphasis on the aspects that included structural properties, synthesis methods and catalytic activity of metal exchanged heteropolyacids. Results: Forty-three papers were included in the references of this mini-review. In almost papers cited discuss the surface and catalytic properties of heteropolyacids. Among the papers, the majority (32) are related to the class of polyoxometalates, in which the Keggin heteropolyacid and its salts were included. Eleven papers describe the physical and chemical properties of metal exchanged Keggin salts as well as the synthesis processes. Twenty-seven papers outline the catalytic activity of heteropolyacid salts in different reactions such as oxidation, Friedel-Crafts acylation, transesterification, hydrolysis and so on. In most of the papers, the effects of Brønsted and Lewis acidities on activity and selectivity of heteropolyacid- based catalysts are discussed. The reactivity of heteropolytungstate and heteropolymolybdate metal transition salts is a central theme of most of the papers (32). Conclusion: The findings of this mini-review confirm that understanding and modulating the physical and chemical properties of heteropolyacid salts comprise a key aspect for obtaining highly active and selective heterogeneous catalysts. Moreover, solid salts of metal exchanged heteropolyacid are attractive options to the solid-supported traditional catalysts.

Background: Au-catalyzed selective oxidation of benzyl alcohol to benzaldehyde was investigated over Au/γ-Al2O3 nanocatalysts under aerobic conditions. The homogeneous depositionprecipitation method was used to prepare these catalysts. In the present work, varying Au content over γ-Al2O3 support has been used as heterogeneous catalysts to investigate the vapor phase oxidation of benzyl alcohol to benzaldehyde. In this study, it was observed that an Au/γ-Al2O3 catalyst shows an optimum conversion of benzyl alcohol to benzaldehyde at Au loading of 2 wt%. The catalytic activity of Au/γ-Al2O3 was interrelated with Au particle size supported by Au on γ-Al2O3 support. The catalytic activity depends on the size of the gold nanoparticles, as well as on the interaction between gold nanoparticles and various support materials. We have optimized various parameters such as Au nanoparticles loading, reaction temperature, and reaction time for efficient conversion as well as product selectivity. Methods: The Au nanocatalysts supported on γ-Al2O3 were prepared with by homogeneous depositionprecipitation (HDP) method by varying the loading of Au nanoparticles and using urea as the precipitating agent. Results: A varying Au loading has been employed over γ-Al2O3 support material after their structural investigation. The vapor phase oxidation of PhCH2OH to PhCHO was investigated over Au/γ-Al2O3 catalysts under air. Only a few percent of benzyl alcohol were found to convert in the absence of assynthesized catalysts. Moreover, bare support also showed a very poor catalytic activity towards benzyl alcohol conversion. Hence, the synergistic effect of Au nanoparticles over support materials facilitated as an excellent catalyst for efficient conversion of benzyl alcohol to benzaldehyde. The 2 wt% of Au/γ- Al2O3 catalysts after 2 h of reaction time showed the maximum conversion of 33%. Conclusion: Au/γ-Al2O3 catalyst prepared by HDP method exhibits a high catalytic activity as well as stability for the vapor phase conversion of benzyl alcohol to benzaldehyde. The optimum condition for efficient conversion of benzyl alcohol is observed to be 2 wt% Au loading, 2 hr reaction time and 320 °C of reaction time for all cases.

Background: Recently sustainable transformations are a challenge for the researchers in areas like health, social sector and environment. To overcome these troubles, it has been planned to produce simple and facile methods to carry organic reaction under mild & eco-friendly conditions. Nano magnetite supported catalysis is a very significant and growing field in catalytic science with application in organic synthesis. Therefore, this research article focuses on the synthesis of nano-magnetite supported cysteine organocatalyst and its application in catalysis and synthetic organic chemistry. Methods: Magnetically recyclable heterogeneous catalyst ferrite-L-cysteine was prepared by simple stirring method in distilled water media without any other reagent followed by dehydration technique. The synthesized catalyst is well characterized by FT-IR, TEM and FEG-SEM-EDS spectroscopy. This functionalised nanocat- Fe-cys was employed in the synthesis of quinolines under Friedlander reaction and also pyrazole derivative under Knoevenagel condensation reaction. The % conversion of products was checked by thin layer chromatography and the synthesized compounds were further confirmed by NMR techniques. Results: To check the competency of synthesized nanocat-Fe-cys for Friedlander & Knoevenagel raction under solvent free conditions, microwave irradiation method employed superiorly over conventional oil bath method. The products were obtained in very clean & noticeably higher yield (81-94%). The catalyst ferrite cysteine was found to be recyclable for ten consecutive run with no significant loss in catalytic activity. Conclusion: In the present research article, the synthesis of highly active, recyclable & versatile organo nanocatlyst ferrite-cysteine using easily available precursor via the simple impregnation procedure is presented. The MNPs was found to be stable under investigated conditions & highly effective in the synthesis of substituted quinolines and pyrazole derivatives. The simple eco-friendly method, mild reaction conditions, economically affordable and good product yields make it an attractive sustainable protocol.

Background: Poly ethylene glycol based dicationic acidic ionic liquid catalysts [PEG-DAIL, Cl] have been prepared by mono chloroacetic acid and used as a cost effective alternative to [PEG1000DAIL, HSO3], a sultone based catalyst. Biginelli reaction is found in a large family of biologically active molecules exhibiting a wide range of important pharmacological properties. Synthesis of 3,4-dihydropyrimidin-2(1H)-ones has been already reported using wide variety of acid catalysts. Method: Three materials were prepared using different molecular weights of PEG. These catalysts are termed as (i) [PEG600-DAIL, Cl] (ii) [PEG1500-DAIL][Cl] and (iii) [PEG4000-DAIL, Cl]. The synthesized material [PEG-DAIL, Cl] were characterized by FT-IR, 1H-NMR, 13C-NMR, ESI-MS, DSC and TGA techniques. The products were further confirmed by the GC-MS and NMR techniques. Results: Synthesized material is acidic in nature, which is proved by pH studies. These materials have good thermal stability and wide range of solubility in different solvents. These catalysts explored for test reaction as Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones as a acid catalyst under mild reaction conditions. Conclusion: The present method provides yet another series of catalysts for the Biginelli reaction. On comparison of initial rate mmol.min-1 and acidity of the catalyst for the said reaction, [PEG1500-DAIL][Cl] shows better results as compared to other two. The catalyst system was found that reusable up to five cycles without much loss in activity. Separation and reuse of this catalyst is simple and economical.

Background: The development of simple yet efficient functionalization protocols has gained considerable importance for the discovery of useful heterocycle compounds, such as isoxazolo, isoindol and their derivatives. 3a-hydroxyisoxazolo[3,2-a]isoindol-8(3aH)-ones are a type of novel heterocycles first reported by Lu group involving Ph3P-catalyzed annulation process. In this work, we aim to explore the synthesis of this novel complex heterocycles using simple base catalyst from internal alkynoates with N-hydroxyphthalimide. Methods: The reactions were conducted in the Schlenk flasks, protected by N2. The products were identified by TLC, and isolated by column chromatography on silica gel (200-300 mesh) using petroleum ether (60-90 °C) and ethyl acetate. All products were characterized by 1H NMR, 13C NMR and mass spectroscopy. Results: A highly active base-promoted system based on NaOAc•3H2O has been designed for the oxa- Michael-aldol [3+2] annulation reactions of internal alkynoates with N-hydroxyphthalimide, giving a series of pharmaceutically attractive 3a-hydroxyisoxazolo[3,2-a]isoindol-8(3aH)-ones in synthetically useful yields of up to 98%. Only 10 mol% NaOAc•3H2O is needed for the reaction at room temperature within 6 h. Besides, a plausible base-promoted intermolecular [3+2] oxa-Michael-aldol type mechanism is proposed. Conclusions: We have demonstrated the simple cascade reaction between alkynoates and NHPI as a facile access to pharmaceutically attractive 3a-hydroxyisoxazolo[3,2-a]isoindol-8(3aH)-ones, with a base-promoted intermolecular [3+2] oxa-Michael-aldol type mechanism. Target heterocycles with various functional groups were achieved in good to excellent yields at room temperature for 6 h. Such a synthetic methodology provides an effective approach of the synthesis of the fused heterocyclics in combination with CO2 utilization.

Background: The asymmetric Michael-Henry cascade reaction of 1,2-dione with nitroolefins is an important method for the preparation of chiral bicycle[3,2,1] octane derivatives, which are useful intermediates for the synthesis of biologically active bicyclo octane skeletal compounds. However, limited success has been achieved so far for ionic liquid supported (ILS) chiral ligands in transition metal catalyzed asymmetric cascade reactions. Methods: The catalyst was generated in situ by the combination of ammonium ILS diamine 6b ligand (3 mol%) with metal salt Ni(OAc)2 (3 mol%) in a solvent dimethylformamide. Then the substrates 1,2- cyclohexadione and nitroolefin were added and the reaction mixture was stirred at room temperature for 0.3-2.7 h. Results: The ammonium ILS diamines were successfully utilized as chiral ligands in Ni(II)-catalyzed asymmetric Michael-Henry cascade reactions between 1,2-cyclohexadione and nitroolefins at room temperature. High yields (80-98%), high diastereoselectivities (up to 47:1) and enantioselectivities (84- 94% ee) were observed for the various bicyclo [3,2,1] octane derivatives containing many functional groups. Conclusion: 1,2-cyclohexadione underwent asymmetric Michael-Henry cascade reaction with nitroolefins in the presence of ammonium ILS diamine/Ni(II) catalyst to give the bicyclo [3,2,1] octane derivatives in high yields with ee ranging from 84-94%. Furthermore, the catalytic system is recyclable.

Background: Thiazoles have been a class of important synthetic heterocyclic compounds which are widely used in clinical therapy. These compounds exhibited biological activities such as antitumor, antifungal, antibiotic, and antiviral properties. Also, applications such as liquid crystals and cosmetic sunscreens have been found for these important structures. Methods: The purpose of this work is to identify the most suitable condition for the synthesis of some thiazole derivatives in the presence of nano-Fe3O4@ZrO2-H3PO4 as magnetically recyclable nanocatalyst that presented as n-FZSA in the presence of the two forms of water (ordinary or magnetized) as solvent. Results: The results showed that n-FZPA exhibited high catalytic activity towards the synthesis of thiazole derivatives, with the desired products being formed in high yields. The catalyst was easily recyclable and could be reused at least three times without any discernible loss in its catalytic activity. Furthermore, this new catalytic method for the synthesis of thiazoles provides rapid access to the desired compounds in high yields in the presence of ordinary or magnetized water upon reflux condition following a simple work-up procedure, and avoids the use of harmful organic solvents. Final outcomes exhibited that magnetized water showed better yields in shorter reaction times at the same conditions. This method therefore represents a significant improvement over the methods currently available for the synthesis of thiazole derivatives. Conclusion: This new method provided some thiazole derivatives via the reaction of acyl chloride with ammonium thiocyanate, amino acides and alkyl bromides catalyzed by n-FZPA in high yields over short reaction time upon refluxing ordinary or magnetized water, following a facile work-up process. Totally, the magnetized water provided a better situation as solvent for this reaction. The catalyst is inexpensive and easily obtained, stable and storable. Also, easy magnetic separation makes this catalyst attractive in view of green chemistry and catalysis science.