Synthesis of 5‐Trifluoromethyl‐4,5‐dihydrooxazoles From Trifluoromethyl(alkenyl)ketones and <i>p</i> ‐Tosylmethylisocyanide

ABSTRACT A simple synthetic approach towards 5‐(trifluoromethyl)‐4,5‐dihydrooxazoles was elaborated. To this end, the reaction of trifluoromethyl(alkenyl)ketones with p ‐tosylmethylisocyanide (TosMIC) in the presence of the base was employed to afford the target heterocycles in good to high yields. The process is characterized by high stereo‐ and chemoselectivity. The stereochemistry of the 4,5‐dihydrooxazoles is unambiguously proved by the combination of NMR and quantum chemical calculational methods. The formation of the oxazole cycle occurs via nucleophilic attack of TosMIC on the carbonyl moiety, followed by intramolecular cyclization with participation of the isocyanide fragment.