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Nanoparticle catalyzed synthesis is a green and convenient method to achieve most of the
chemical transformations in water or other green solvents. Nanoparticle ensures an easy isolation process
of catalyst as well as products from the reaction mixture avoiding the hectic work up procedure.
Zinc oxide is a biocompatible, environmentally benign and economically viable nanocatalyst with effectivity
comparable to the other metal nanocatalyst employed in several reaction strategies. This review
mainly focuses on the recent applications of zinc oxide in the synthesis of biologically important
heterocyclic molecules under sustainable reaction conditions.
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Application of zinc oxide in organic synthesis: Considering the achievable advantages of this nanocatalyst,
presently several research groups are paying attention in anchoring zincoxide or its modified
structure in several types of organic conversions e.g. multicomponent reactions, ligand-free coupling
reactions, cycloaddition reaction, etc. The advantages and limitations of this nanocatalyst are also
demonstrated. The present study aims to highlight the recent multifaceted applications of ZnO towards
the synthesis of diverse heterocyclic motifs. Being a promising biocompatible nanoparticle, this catalyst
has an important contribution in the fields of synthetic chemistry and medicinal chemistry.
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C-C or C-heteroatom bond formation from direct C-H bond activation of several heteroarenes containing suitable directing groups has now emerged as an efficient and straightforward strategy for the design of complex heterocyclic molecules as well as their late-stage functionalization. The most common problem of several C-H bond activation reactions is high temperature, long reaction time and unwanted side reactions where recent examples of MW assisted C-H bond activation showed the requirements of low temperature and short completion time and thus proved its efficacy in terms of heating effect and conversion rate of conventional heating methods. The schemes discussed in the present review depict the reaction conditions along with a look into the mechanism involved to render a deep understanding of the catalytic role of palladium-catalysis. In some examples, the optimization procedure of the corresponding strategy has been illustrated through tables, i.e., choice of catalyst, solvent screening, loading of the catalyst and percentage yield with different substrates. Each of the described illustrations has been analyzed considering a wide variety of reactants, reaction conditions, and transition metals employed as the catalyst. This review definitely allows to introduce the synthetic chemists in understanding the challenges associated with the previous methods as well as their drawbacks and future opportunities in choosing substrates, catalyst and reaction conditions. This review would be alluring to a wider range of synthetic chemists in academia and industrial R&D sectors working with heterocyclic chemistry. In this short perspective, an outline of recent eloquent examples of a variety of palladium-catalyzed C-H bond activation involving bio-oriented heterocycles achieved in the past ten years is nicely presented and the pros and cons of each strategy are highlighted so that the researchers could get enough scope for further designing and modification of developed protocols.
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