Transition metal-free direct trifluoromethylation of 2,3-Dihydropyridin-4(1H)-ones at room temperature

A transition metal-free, regioselective C-5 trifluoromethylation of 2,3-dihydropyridin-4(1H)- ones (cyclic enaminones) with trimethyl(trifluoromethyl) silane (TMSCF₃) was developed that proceeds under mild conditions at room temperature. This direct transformation was successful with both electron-rich and electron-deficient cyclic enamin- ACHTUNGTRENUNGones. This method bypasses substrate prefunctionalization and transition metal catalysis, and allows the convenient and direct access to a variety of medicinally important 3-trifluoromethylpiperidine derivatives. This chemistry also represents a rare example of a direct trifluoromethylation of an internal olefinic C-H bond. A radical mechanism is proposed for this reaction.