Umpolung of Indoles: Triflic Acid-Mediated C3-Regioselective Hydroarylation of N-H Indoles

The direct dearomative addition of arenes to the C3-position of unprotected indoles is reported under operationally simple condi-tions, using triflic acid at room temperature. The present regioselective hydroarylation is a straightforward manner to generate an electrophilic indole at the C3-position without the need of a deactivating acetyl group at the indolic nitrogen as in previously reported strategies. This atom economical method delivers biologically relevant 3-arylindolines and 3,3-spiroindolines in high yields and regioselectivities from both intra- and intermolecular processes. DFT computations suggest the stabilization of cationic or dicationic intermediates with H-bonded (TfOH)n clusters.