Trifluoroacetic Acid Promotes Umpolung of 2‐Methylindole to Achieve C(sp3)‐H Activation

An umpolung strategy for the C(sp3)‐H aminomethylation of 2‐methylindole has been developed using trifluoroacetic acid to induce the transformation, with aminals serving as precursors of iminium ion. Mechanistic studies have clearly shown that trifluoroacetic acid may play a pivotal role in this strategy. The utilization of readily available starting materials, mild reaction conditions, tolerance to complex functional groups, combine with yields of up to 98% and potential biological applications render this protocol applicable and useful for organic synthesis and medicinal chemistry.