Acid-promoted cyclization of 2,4-diaryl-1,1,1-trifluorobut-3-en-2-oles and their TMS-ethers into CF₃-indenes

Abstract

2,4-Diaryl-1,1,1-trifluorobut-3-en-2-oles and their TMS-ethers in HSO at room temperature in just 2 min are quantitatively cyclized into 1-aryl-3-trifluoromethyl-1H-indenes. The reaction proceeds through an intermediate formation of the corresponding CF-allyl cations, which are cyclized regioselectively at the allyl carbon atom most remote from the CF-group. The obtained CF-indenes in solution of EtOAc in the presence of silica gel at room temperature over 4 h are quantitatively isomerized into 3-aryl-1-trifluoromethyl-1H-indenes.

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.…”

Reactions of 1,5-Diaryl-3-(trifluoromethyl)pent-1-en-4-yn-3-yl Cations with Benzene in TfOH. Synthesis of CF3-“Helicopter”-Like Molecules

“…Based on our recent transformations − of trifluoromethyl-substituted carbocations generated from CF 3 -allyl alcohols in Brønsted superacids (CF 3 SO 3 H, FSO 3 H), or Lewis acids (FeCl 3 , AlCl 3 , AlBr 3 ), we undertook a study of the reactions of TMS ethers of 1,5-diaryl-3-(trifluoromethyl)­pent-1-en-4-yn-3-oles ( 1 ) in the superacid CF 3 SO 3 H (TfOH) (Scheme ).…”

TfOH-Promoted Reaction of 2,4-Diaryl-1,1,1-Trifluorobut-3-yn-2-oles with Arenes: Synthesis of 1,3-Diaryl-1-CF3-Indenes and Versatility of the Reaction Mechanisms

“…It should be noted that many of the reactions studied lead to the exclusive formation of only one of CF 3 -indene 4 or 5 in good yields. Such CF 3 -indenes are rather rare substrates, and there are only a few reports on their synthesis [39,40,41,42,43,44].…”