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A transition metal-free, regioselective C-5 trifluoromethylation of 2,3-dihydropyridin-4(1 H)-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 enaminones. 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. [ABSTRACT FROM AUTHOR]

A green and mild protocol for the dehydrogenative olefination of cyclic enaminones was devised via palladium catalysis at room temperature using oxygen as the terminal oxidant. The synthetic utility of the olefinated cyclic enaminones afforded a series of unique 1,3,5-trisubstituted benzenes via an unanticipated Diels-Alder tandem reaction. The broad substrate scope and good yields achieved with this new protocol provide an alternative pathway for arene functionalization.