A mild strategy for Co(III)-catalyzed C(sp2)–H cyanation of indoles was developed by using NCBLD as an electrophilic cyanation reagent and 1-butyl-3-acetylimidazole ditrifluoromethylsulfonimide ([BAIM]NTf2) as an environmentally friendly and recyclable solvent, and a series of 2-cyano products were obtained at room temperature. Adopting this strategy, the unnatural nucleotide fragment precursor of