The Mn-catalyzed C–H alkenylation reactions of indole with terminal- and internal-alkynes have been developed. In the presence of a catalytic amount of acid, the procedure efficiently affords bis/trisubstituted indolyl-alkenes in a highly regio- and stereo-selective manner. Without the addition of acid, the reaction undergoes a [2+2+2] cyclization process to give carbazoles with release of hydrogen gas. Notably, the directing pyrimidyl group can be readily removed. Experimental studies reveal that the reaction is initiated by a C–H activation step and the acid is the selectivity controller via a hydrogen transfer process.

An unprecedented catalyst-free formylation of amines using CO₂ and hydrosilanes was developed.