Diastereoselective Synthesis of 6-Trifluoromethyl-5,6-dihydropyrans via Phosphine-Catalyzed [4+2] Annulation of α-Benzylallenoates with Ketones

The highly diastereoselective synthesis of 6-trifluoromethyl-5,6-dihydropyrans was realized by the phosphine-catalyzed [4 + 2] annulation of ethyl alpha-benzylallenoates and trifluoromethyl ketones.