Progress in Annulative Transformations from Indoles to Carbazoles: State of the Art

Carbazole is an important type of nitrogen organic compound containing aromatic heterocyclic ring. Carbazole derivatives are endowed with unique physical and chemical properties, and applied to natural products, various pharmacological activities, many drugs and photophysical materials. The concise and versatile synthetic strategies of ubiquity of carbazole analogues have attracted significant attention from the synthetic chemists. Herein, the current progress of annulation transformations from indoles to carbazole derivatives is summarized in recent 5 years. The representative samples of the cyclization strategies have been selected and divided into three types, respectively: [2+2'+2'] cyclization reaction, [2+2'+2"] cyclization reaction and [4+2] cycloaddition. The basic properties, advantages and limitations of each reaction are discussed in detail. A perspective is also given in this review.