Triflic Acid as an Efficient Brønsted Acid Promoter for the Umpolung of N‐Ac Indoles in Hydroarylation Reactions

Abstract We report that triflic acid, a strong Brønsted acid, is a very powerful alternative to FeCl 3 to mediate the hydroarylation of N−Ac indoles, which delivers regioselectively 3‐arylindolines, 3,3‐spiroindolines or 2‐arylindolines. Mechanistic explorations point towards the existence of a highly electrophilic intermediate by simultaneous activation of the acetyl and of the C2=C3 bond by protons. magnified image