Radical denitrogenative transformations of polynitrogen heterocycles: Building C–N bonds and beyond

Abstract

Polynitrogen heterocycles are readily available and have recently arisen as versatile synthons for the formation of various C–C and C–X bonds, and medicinally active nitrogen-containing heterocycles. Several cascade reactions, including annulation, radical cascade, and borylation reactions, have been reported in which polynitrogen heterocycles are applied as arylation reagents. The success of these exceptional reactions illustrates the great synthetic potential of polynitrogen heterocycles, which provides a direct and useful approach to arylation reactions and the synthesis of nitrogen-containing heterocycles. The use of photocatalysts to effectively transfer energy from visible light to non-absorbing compounds has gained increasing attention as this method allows for the mild and efficient generation of radicals in a controlled manner. This approach has thus led to new methods that involve unique bond formation reactions. In addition, the use of free radical intermediates stabilized by transition metal catalysts is a powerful way to construct new chemical bonds. The aim of this review is to highlight the rapidly expanding area of radical-initiated denitrogenative cascade reactions of polynitrogen heterocycles and elaborate on their mechanisms from a new perspective by using photocatalysis and metal-based catalysis.