Salicylaldehyde-Enabled Co(II)-Catalyzed Oxidative C-H Alkenylation of Indoles with Olefins

A ligand-promoted oxidative dehydrogenation C-H alkenylation of indoles and olefins was achieved using commercial and low-cost Co(NO3)2<middle dot>6H2O as a catalyst and Mn(OAc)2 as an oxidant. The design and selection of electrically unique methyl-substituted salicylaldehyde as a ligand is the key to achieve this transformation. This protocol can introduce an indole backbone into diverse bioactive molecules such as ibuprofen, naproxen, and Estrol for late-stage synthetic modification, which has potential applications in the discovery of drug molecules containing an indole motif.