Synthesis of 3-phenyl-5-(trifluoromethyl)isoxazole and 5-phenyl-3- (trifluoromethyl)isoxazole

Reaction of 4,4,4-trifluoro-1-phenyl-1,3-butanedione with hydroxylamine led to the formation of 5-hydroxy-3-phenyl-5-(trifluoromethyl)-4,5-dihydroisoxazole which was dehydrated to 3-phenyl-5-(trifluoromethyl)isoxazole. This isomer can also be synthesized by reaction of 4-chloro-4-phenyl-1,1,1-trifluoro-3-buten-2- one with sodium azide. The regioisomer, 5-phenyl-3-(trifluoromethyl)isoxazole was synthesized by reaction of 1,1,1-trifluoro-4-phenylbut-3-yn-2-one with hydroxylamine and by the reaction of 3-chloro-1-phenyl-4,4,4-trifluorobut-2-en- 1-one with sodium azide. Both isomers were characterized by mass and NMR spectroscopy.