Recent Progress on Pyridine N‐Oxide in Organic Transformations: A Review

Abstract

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.

N‐Pyridylureas as Masked Isocyanates Fort the Late‐Stage Diversification of Pyridine‐N‐Oxides

“…[1] Most often, they are important substrates in organic synthesis. Particularly, their functionalization via both transition metal-catalyzed [2][3][4] and metal-free [5][6][7][8][9][10][11] reactions, as well as light-mediated [12] processes has been well studied. However, the significance of N-oxides does not exhaust only this role.…”

Mechanism and Enantioselectivity in QUINOX-Catalyzed Asymmetric Allylations of Aromatic Aldehydes: Solvent and Substituent Effects

“…Pyridine N -oxides have garnered significant attention due to their versatile utility as electro-pair donors, mild oxidants, and ligands in metal complexes. − In particular, they act as Lewis acid catalysts for a range of important chemical transformations. These transformations include the allylation and propargylation of aldehydes, − the cyanosilylation of imine derivatives, and the opening of epoxides with silicon tetrachloride. , Among these, the enantioselective allylation of aldehydes using allyltrichlorosilanes (as depicted in Scheme .)…”

Selectivity in Catalytic Asymmetric Formal [3 + 3] Annulation of 2-Enoyl-pyridine N-Oxide with Benzyl Methyl Ketone

“…N-oxides obtained in the enantiomerically enriched form are successfully used as chiral ligands or organocatalysts in asymmetric synthesis [9][10][11]. Aza-aromatic N-oxides have significant synthetic value due to their unique properties resulting from the presence of the N + -O − bond in their structure [12][13][14]. In this last context, particularly interesting are heteroaromatic N-oxides having several places in their structure susceptible to transformations, preferably asymmetric ones, and allowing for significant and sterically controlled expansion of the skeleton [15][16][17][18][19].…”