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Trimethylsilyl ethers of 1,5-diaryl-3-(trifluoromethyl)-pent-1-en-4-yn-3-oles [Ar–C≡C–C(CF3)(OSiMe3)–CH═CH–Ar′] in the superacid TfOH give rise to reactive conjugated CF3-allylic-propargylic cation...

The reaction of TMS-ethers of 2,4-diaryl-1,1,1-trifluorobut-3-en-2-ols with arenes in TfOH at room temperature for 5 min results in the formation of trans-/cis-1,3-diaryl-1-trifluoromethyl indanes in good yields (up to 99%). The predominant or exclusive formation of indanes with a trans-configuration of 1,3-diaryl groups has been observed. The reaction proceeds through an intermediate formation of the corresponding mesomeric CF3-allyl cations. A plausible reaction mechanism is discussed.

The reaction of CF3-propargyl alcohols [ArCCCH(OH)CF3] with arenes under the action of acidic HUSY zeolite CBV-720 was investigated. It was found that the reaction at 100 °C for 1 h gave rise to 3-aryl-1-CF3-indenes in up to 83% yield. Electronic characteristics of the reaction key intermediates, mesomeric CF3-propargyl-allenyl cations [ArCC−HC+(CF3) ↔ ArC+CCH(CF3)], were studied by DFT calculations. A plausible cationic reaction mechanism is discussed.

Reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-ols with benzene in the presence of HUSY acidic zeolite (CBV-720) at 100°C in 1 h (glass high-pressure reactor) led to the formation of 1,3-diaryl-1-trifluoromethylindenes in 39–92% yield. A probable reaction mechanism was proposed, which involves formation of the corresponding trifluoromethyl-substituted propargyl cations.

Trimethylsilyl ethers of 1,5-diaryl-3-(trifluoromethyl)pent-1-en-4-yn-3-oles in superacid CF3SO3H (TfOH) give rise to the corresponding intermediate CF3-pentenynyl cations. These species react with benzene to afford conjugated CF3-pentenynes, which undergo subsequent cyclization, first, into CF3-cycloheptadienes and, finally, into unusual CF3-“helicopter”-like bicyclic structures.

1,4-Diacyl-5-methyl-1H-pyrazoles on heating in toluene undergo isomerization to 1,4-diacyl-3-methyl-1H-pyrazoles via intermolecular N → N acyl group migration. 1,4,5-Trisubstituted pyrazoles obtained by reaction of 2-ethoxymethylidene derivatives of 1,3-diketones with 1,3-benzothiazol-2-ylhydrazine or phenylhydrazine failed to isomerize to 1,3,4-trisubstituted pyrazoles.

Carbonic dihydrazide reacted with 2 equiv of trifluoroacetylacetone to give a compound containing 5-hydroxy-4,5-dihydropyrazole and keto enehydrazine fragments. Analogous 2 : 1 condensations of trifluoro-acetylacetone and 4-ethoxy-1,1,1-trifluorobut-3-en-2-one with oxalohydrazide and malonohydrazide afforded bis(5-hydroxy-4,5-dihydropyrazole) structures as two diastereoisomers.

The TfOH-mediated reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-oles (CF3-substituted diaryl propargyl alcohols) with arenes in CH2Cl2 afford 1,3-diaryl-1-CF3-indenes in yields up to 84%. This new process for synthesis of such CF3-indenes is complete at room temperature within one hour. The synthetic potential, scope, and limitations of this reaction were illustrated by more than 70 examples. The proposed reaction mechanism invokes the formation of highly reactive CF3-propargyl cation intermediates that can be trapped at the two mesomeric positions by the intermolecular nucleophilic attack of an arene partner with a subsequent intramolecular ring closure.