Transition-Metal-Free Synthesis of Carbazoles and Indoles by an SNAr-Based "Aromatic Metamorphosis" of Thiaarenes

Dibenzothiophene dioxides, which are readily prepared through oxidation of the parent dibenzothiophenes, undergo nucleophilic aromatic substitution with anilines intermolecularly and then intramolecularly to yield the corresponding carbazoles in a single operation. The “aromatic metamorphosis” of dibenzothiophenes into carbazoles does not require any heavy metals. This strategy is also applicable to the synthesis of indoles. Since electron‐deficient thiaarene dioxides exhibit interesting reactivity, which is not observed for that the corresponding electron‐rich azaarenes, a combination of a thiaarene‐dioxide‐specific reaction with the SNAr‐based aromatic metamorphosis allows transition‐metal‐free construction of difficult‐to‐prepare carbazoles. Lite on the metal: Dibenzothiophene dioxides undergo sequential inter‐ and intramolecular nucleophilic aromatic substitution with anilines to yield the corresponding carbazoles in a single operation. One advantage of this protocol is that heavy metals are not required. Coupling a thiaarene‐dioxide‐specific reaction with the SNAr carbazole synthesis allows construction of difficult‐to‐access carbazoles.