Current Organic Chemistry - Volume 21, Issue 8, 2017

Synthesis of varied N-heterocycles and C-N bond forming reactions catalyzed by novel proficient heterogeneous Cu-based solid catalysts namely, CuI-zeolites, CuII-HT, and CuII-PMOs are addressed in this review article. The above-mentioned catalysts have been proved to be remarkable heterogeneous catalysts for many organic transformations mostly, one-pot MCRs including synthesis of 1,2,3-triazoles through 1,3-dipolar cycloaddition and 2H-indazoles over heterocyclization of C-N and N-N bond formations and range of C-N bond forming reactions. These novel synthetic methods offered many advantages including shorter reaction times, simple reaction procedures, catalyst recyclability, good to moderate yields, and broader substrate scope. All the aspects related to these approaches are addressed in this comprehensive review.

In recent years, mesoporous silica materials with controllable structure, tunable porosity and high surface area have been widely studied with regard to applications as excellent adsorbents and heterogeneous catalysts. SBA-15 is among the most attractive mesoporous silicas due to its adjustable pores and thick pore walls. Grafting various organic compounds on the surface of SBA-15 can improve the catalytic activity of silica surface. In this regard, SBA-15 has been functionalized with amine groups to create a promising candidate in catalysis of various kinds of organic reactions. Amino-functionalized mesoporous SBA-15 (SBA-Pr-NH2) has been found to be useful for base-catalyzed reactions. SBA-Pr-NH2 exhibits efficient catalytic activity as a heterogeneous reusable green catalyst in organic transformations. This catalyst can be easily removed from the reaction mixture by simple filtration, recovered and reused without significant loss of activity. This overview covers the recent achievements in the application of amino-functionalized SBA-15 as a green catalyst.

Apatites, minerals that are involved in numerous applications in chemistry, biochemistry and medicine have shown important catalytic properties and are emerging as powerful catalysts in various organic reactions (oxidation, C-C bond formation, cycloaddition, N-Arylation, epoxidation, water gas shift reaction, hydroformylation, CH4 coupling reaction….). Apatites, in which the composition and surface properties can be tuned by replacing anions or cations in their structures, leading to a large spectrum of compositions, can also be used as macroligands to support catalytic active centers. In this review we emphasize the creation of a large variety of modified apatites, and describe their structures and properties as well as their catalytic activities.

With the increasing environmental and societal concerns about global warming associated with carbon emission, great efforts have been devoted to carbon dioxide fixation during the past two decades. Indeed, CO2 has been widely used as a potential C1 building block for the production of various chemical products, as it is nontoxic, renewable, economical and abundant. One promising methodology is the coupling reaction of CO2 with aziridines to afford oxazolidinones, which is 100% atom-efficient and eco-friendly. In addition, oxazolidinones are important heterocyclic compounds showing application as intermediates and chiral auxiliaries in organic synthesis. To date, numerous homogeneous catalysts have been developed for this reaction. With criteria of green chemistry and sustainable development, developing efficient heterogeneous catalysts would be crucial for industrial application. In this review article, we present the latest progress on the coupling reaction of CO2 with aziridines, and particularly focus on the preparation, activity evaluation and recyclability of various heterogeneous catalytic systems including mesoporous material, functionalized polymer-based catalysts and supported catalysts. We hope this review could stimulate further research on oxazolidinone synthesis from CO2 and aziridines with green, and efficient heterogeneous catalyst.

Sonogashira coupling reactions demonstrates an efficient and facile methodology for C(sp)-C(sp2) bond formations via transition-metal-catalyzed processes and have found applications in a wide variety of areas including medicinal chemistry, agrochemistry, materials, electronics and synthesis of natural products, biologically active molecules, heterocycles, dendrimers and conjugated polymers or nanostructures. In recent years, nanosized heterogeneous catalysts have been widely studied for the above reactions due to thermal stability, reusability and high catalytic activities. In this review, we present an introduction to the subject of carbon-carbon bond formations and recent efforts in the preparation and application of heterogeneous nanocatalysts for Sonogashira coupling reactions. The scope, limitations, and green aspects of the reactions, convenient methods of preparation of heterogeneous nanocatalysts and their characterization have also been highlighted. These include metal nanoparticles, nanoclusters and nanocrystals, bimetallic, trimetallic and core-shell nanoparticles, polymersupported metal nanoparticles, carbon- or graphene-supported metal/metal oxide nanohybrids and metal-organic frameworks Pd catalysts. Numerous examples demonstrated the use of effective supports such as silica, SBA-15, MCM-41, BaO, Smopex®, ZnO, celluloses, montmorillonite, Al²O³, chitosan and natural biomaterials in Sonogashira coupling reactions. This work is dedicated to the 45 years of frankly attempts of Professor Ali Akbar Entezami to the education and development of chemistry in Iran.