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

The reaction of trifluoroacetyl alkynes [ArC equivalent to 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.