Skeletal Formation of Carbocycles with CO2: Selective Synthesis of Indolo[3,2-b]carbazoles or Cyclophanes from Indoles, CO2, and Phenylsilane

The catalytic reactions of indoles with CO2and phenylsilane afforded indolo[3,2-b]carbazoles, where the fused benzene ring was constructed by forming two C–H bonds and four C–C bonds with two CO2molecules via deoxygenative conversions. Nine-membered cyclophanes made up of three indoles and three CO2molecules were also obtained, where the cyclophane framework was constructed by forming six C–H bonds and six C–C bonds. These multicomponent cascade reactions giving completely different carbocycles were switched simply by choosing the solvent, acetonitrile or ethyl acetate.