Pd(II)-Catalyzed Synthesis of Tetrahydrocarbazoles and 3-Substituted Indoles

Significance

A palladium(II)-catalyzed synthesis of tetrahydrocarbazoles and 3-substituted indoles from simple indole derivatives, with demonstrated potential for the preparation of larger and heterocyclic annulated rings, is reported. Moderate to excellent yields and diastereoselectivities are observed in the cyclization reaction which is proposed to occur via normal C-3 electrophilic reactivity of the indole on a Pd-olefin complex to generate a spiro intermediate, regioselective migration, followed by CO insertion and methanolysis of the resulting acyl palladium intermediate. The scope of reaction includes annulated bicyclic and 7-membered ring products as well as annulated pyrroles and β-carbolines. Mechanistic studies using deuterated olefins were carried out.