Photochemistry of Aromatic Azides: Relationship Between Substituents, Intermediates and Reactivity

Abstract

Aromatic azides are high-energy compounds that decompose easily with light. In recent decades, they have found diverse applications in organic chemistry, biochemistry, materials science and medicinal chemistry. For a better application of these compounds, it is important to understand their basic photochemistry. Aromatic azides photochemical reactions have fascinated researchers for more than a century. Spectroscopists have investigated the intermediates formed using conventional and high-resolution techniques. Theoretical chemists have investigated the intrinsic interplay of several intermediates generated under different experimental conditions. Irradiation of the simplest phenyl azide induces the generation of several intermediates such as triplet nitrene, singlet nitrene, benzazirine, azepine or phenyl nitrenium ion. The placement of different substituents in the aromatic ring modifies the intermediates generated as well as the mechanistic pathways available for a given aryl azide. In this review, the photochemistry of the parent azide and other aromatic azides containing nitro, fluoro or amino substituents will be discussed to determine the relationship between substituents, intermediates and reactivity.