Diazo Retention Transformations of Aryldiazonium Salts Towards Nitrogen-Rich Heterocycles

Abstract

Developing novel synthetic methodologies to access fused nitrogen heterocycles is an active research area of organic chemistry for several decades. Due to their valuable contribution of N-fused heterocycles in organic synthesis, medicinal chemistry, and material research, tremendous efforts have been devoted towards the construction of N-heterocyclic scaffolds.Aryldiazonium salts are ubiquitous class building blocks/reagents widely used in organic synthesis owing to their distinct electrophilic nature to undergo substitution reaction with concurrent loss of molecular nitrogen (C-C, C-N bond formations). Conversely, a distinctive category of reactions known as "nitrogen retention reactions" preserve the diazonium-derived "N2" atoms in the end products. These classes of reactions are of great important due to their uniqueness in constructing nitrogen-rich heterocycles and azo compounds without sacrificing the -N=N-functionality. In this review, we have discussed a range of synthetic methodologies reported over the past ten years (2015-till date) in which aryldiazonium salts are used as a key precursor and the characteristic nitrogen moiety is retained in the N-heterocyclic frameworks. This comprehensive report explored the azo-retention reactions developed under thermal, transition metal catalysed, photochemical and electrochemical conditions. The scope, limitations, mechanism, and post synthetic transformations are specially emphasized.