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1,3-Bis(trifluoromethyl)prop-2-ene 1-iminium triflate salts were prepared for the first time and some synthetic applications as 1,3-biselectrophilic building blocks were established. They were found to react with dimethoxybenzenes or methylene-1,2-dioxybenzenes to furnish vinylogous trifluoroacetylation products (4-aryl-1,1,1,5,5,5-hexafluoropent-3-en-2-ones) and 1-dialkylamino-1,3-bis(trifluoromethyl)-1H-indenes. With aniline and ring-substituted anilines, 2,4-bis(trifluoromethyl)quinolines were formed. An unusual 4H-pyran, formally a condensation product of the N,N-dimethyl-1,3-bis(trifluoromethyl)prop-2-en-1-iminium ion and its enaminone precursor, is also reported.

3-(Trifluoromethyl)prop-2-yne 1-iminium triflate salts were generated from 3-trifloxy-3-(trifluoromethyl)prop-2-ene 1-iminium salts by triethylamine-assisted elimination of triflic acid and trapped in situ in various cycloaddition reactions. 3-(Trifluoromethyl)prop-2-yne 1-iminium triflate salts were generated from 3-trifloxy-3-(trifluoromethyl)prop-2-ene 1-iminium salts by triethylamine-assisted elimination of triflic acid and trapped in situ in various cycloaddition reactions. These included Diels-Alder reactions with 1,3-dienes, [2+2] cycloaddition with 1,4-diphenylbuta-1,3-diene, and [3+2] cycloaddition with organoazides. All these reactions revealed the excellent dienophilic and dipolarophilic reactivity of the electrophilic C,C triple bond of the novel 3-CF3-propyniminium salts., publishedVersion

3-Aryl-1-(trifluoromethyl)prop-2-yn-1-iminium triflate salts represent a novel, highly reactive class of acetylenic iminium salts. Herein we present several reactions which are based on the electron-poor acetylenic bond and on the high electrophilicity of the CF3-substituted iminium group. These salts were found to be highly reactive dienophiles in Diels–Alder reactions with cyclopentadiene, 2,3-dimethylbutadiene and even anthracene. At higher temperature, the cycloadducts undergo an intramolecular SE(Ar) reaction leading to condensed carbocycles incorporating a 1-(trifluoromethyl)-1-(dimethylamine)indene ring system. With styrenes and some substituted styrenes, cascade reactions take place, which likely include cyclobutene and several cationic intermediates and mainly yield 2-(1-phenylvinyl)indenes. In a similar reaction cascade, a fulvene derivative was obtained with 1,4-diphenylbutadiene as the substrate.

Acetylenic iminium triflates with the general formula [R–C≡ C–C(Ar)=N+R2 TfO−] were found to be excellent dipolarophiles in [3+ 2] cycloaddition reactions with diazoacetates leading to (1H-pyrazol-3(5)-yl)methanaminium triflates in high yields. The terminal acetylenic iminium salt (propyne iminium salt) [HC≡C–C(Ph)=N+Me2 TfO−] reacted with an equimolar amount of methyl diazoacetate instantaneously at 20°C to form the expected pyrazole in almost quantitative yield. When a 2:1 stoichiometry was applied, subsequent Michael addition of the pyrazole at the alkyne occurred and the bis(iminium) ditriflate 4 was obtained in high yield. By hydride reduction or hydrolysis of the iminium group, some of the highly hygroscopic pyrazole iminium salts were converted into neutral, twofold functionalized, di- and tri-C-substitued 1H-pyrazoles.