Nowadays heterocyclic compounds are widely used in medicinal chemistry and industry to develop life-saving drugs and medicines. Imidazole is one of the pharmacologically important heterocyclic motifs found in widely used and well-known medicines and bioactive molecules. The applications of imidazole derivatives displaying various biological activities, motivated researchers for the development of more potent and significant drugs containing imidazole moieties. The formation of imidazole derivatives can be achieved using imidazole N-oxide as starting material. In this review, the scope of substrates and reaction mechanisms of various synthetic approaches using imidazole N-oxides as substrates are summarized so that the chemists, researchers, and pharmaceutical industries find its effectiveness in near future for the synthesis of potent, novel, and non-toxic drug molecules.

Quinoline derivatives are very widely known biologically active heterocyclic compounds, as for example quinine, mefloquine, etc. In recent years, the interests of researchers are growing to look for a methodology using quinoline N-oxides as a precursor to make several bio-active quinoline compounds as quinoline N-oxides are more reactive with good regioselectivity than unoxidized quinolines. In this review, numerous procedures are discussed using quinoline N-oxides as a versatile precursor in organic transformations, such as alkenylation, alkylation, arylation, amination, amidation, halogenation and so on under metal or metal-free conditions at C-2, C-3 or C-8 positions. The main focus of this context is to explore various procedures of synthesis of quinoline derivatives with good regioselectivity, to understand the extent of usefulness of those procedures through the study of scope of substrates and the reaction mechanisms of the processes.

Pyridine derivatives are one of the most important moieties in the synthesis of various biologically active compounds containing heterocyclic ring. But, due to the low reactivity of pyridine, pyridine N‐oxides were used as a reactant to develop some bio‐active pyridine derivatives in good amount of yields with high regioselectivity. For that reason, synthesis of various substituted pyridine N‐oxides grabbed the attention of many chemists due to their importance in the formation of various bioactive moieties and their application in various fields like it can be used as a catalyst, oxidant etc. This review is focused on various C−H activation reactions like arylation, acylation, alkylation, alkenylation, cross‐coupling reactions and halogenation reactions in both metal‐catalysed and metal‐free pathway along with their probable mechanism and reaction scopes. The main focus of this review is to discuss about versatile synthetic pathways of pyridine and pyridine N‐oxide derivatives using pyridine N‐oxides as a substrate as well as their mechanistic studies and the scope of the reactions. Besides all of that, this review also discussed about the application (e. g., catalyst) of pyridine N‐oxides in various organic transformation.

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