Indole-to-Carbazole Strategy for the Synthesis of Substituted Carbazoles under Metal-Free Conditions

An efficient indole-to-carbazole strategy has been developed under metal-free conditions. This carbazole formation was highly promoted by NH4I with high regioselectivity through formal [2 + 2 + 2] annulation of indoles, ketones, and nitroolefins. It thus conveniently enabled the assembly of a large number of diversified carbazole products with good tolerance of a broad range of functional groups.