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

Abstract

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.

Generation and NMR Study of Short-Lived and Reactive Trifluoroalkyl Carbocations of the α-Halogenothiophene Series in Brønsted Superacids: Reactions of the Cations with Arenes

“…Based on our previous work on electrophilic activation of organic compounds, , especially on reactions of CF 3 -substituted derivatives, − we undertook a special study on transformations of trifluoroalkyl-substituted halogenothiophenes under the action of Brønsted superacids. The main goal of this work was to investigate reactions of 2-halo-5-(1′-Me 3 SiO-1′-trifluoromethyl-alkyl)­thiophenes 1a – c (see Scheme ) with arenes in the superacid CF 3 SO 3 H (triflic acid, TfOH) and to study by NMR the cationic intermediate species to clarify the reaction mechanisms.…”