Regiocontrolled Hydroarylation of (Trifluoromethyl)acetylenes in Superacids: Synthesis of CF3-Substituted 1,1-Diarylethenes

The reactions between aryl(trifluoromethyl)‐substituted alkynes and arenes in triflic and fluorosulfonic acids were investigated. These reactions proceeded 100 % regioselectively to give 1,1‐diaryl‐2‐trifluoromethylethenes in high yields. Depending on the workup conditions, 3,3,3‐trifluoro‐1,1‐diarylpropan‐1‐ol was also detected in the product mixture. The reaction mechanism was studied by both spectroscopic and theoretical methods. The highly reactive nature of the trifluoromethylated vinyl cations was confirmed by DFT calculations. The stable 2,2,2‐trifluoroethylated carbocation reaction intermediates were observed by 1H, 13C, and 19F NMR spectroscopy. Under treatment with aluminium bromide, the reaction of 3,3,3‐trifluoro‐1‐phenylpropyne with benzene formed 1,3,3‐triphenylindene. The hydration of aryl(trifluoromethyl) alkynes in sulfuric or trifluoroacetic acids smoothly produced 2,2,2‐trifluoroethyl ketones in high yields. The superacidic generation of vinyl cations from aryl(trifluoromethyl)acetylenes was effectively performed using triflic and fluorosulfonic acids under mild conditions. These vinyl cations underwent a subsequent reaction with various arenes to give the corresponding alkenes and alcohols in high yields. The formation of these trifluoroethylated carbocations was confirmed by NMR spectroscopy.