Reactions of Trifluoroacetyl Alkynes Under Electrophilic Activation with Brønsted Acids or Acidic Zeolites

The reaction of trifluoroacetyl alkynes [ArC≡C(C=O)CF₃] with H₂SO₄ or TfOH affords products of addition of the acids to the acetylene bond. Hydrolysis of these adducts results in the formation of the corresponding 1,3‐diketones existing in form of enols [Ar(HO)C=CH(C=O)CF₃] in up to 98 % yield. The application of less acidic TfOH‐pyridine system permits transformation of these alkynes into the corresponding vinyl triflates in up to 76 % yield. Moreover, this reaction is totally stereoselective to give only Z‐configured vinyl triflates. The reaction of trifluoroacetyl alkynes with arenes in TfOH or under the action of acidic HUSY zeolites CBV‐720 gives rise to 1,3‐diaryl‐1‐CF₃‐indenes in up to 81 % yield. Electronic characteristics of initial intermediate mono‐ and dicationic species derived from such alkynes in the highly acidic media were studied by DFT calculations. Plausible cationic reaction mechanism was proposed.