Diels–Alder reactions of trifluoromethyl alkenes with 5-ethoxyoxazoles: synthesis of trifluoromethylated pyridine derivatives

Cycloaddition reactions between 5-ethoxyoxazole derivatives [2,4-dimethyl 5-ethoxyoxazole and 4-methyl 5-ethoxyoxazole] and various trifluoromethyl alkenes [ethyl 4,4,4-trifluorocrotonate CF3CHCHCO2Et, 3,3,3-trifluoro 1-(phenylsulfonyl)-1-propene CF3CHCHSO2Ph and 2-(trifluoromethyl) propenoic acid CF3(HO2C)CCH2] gave several trifluoromethyl-substituted pyridine systems in moderate yield (20–56%). Their structures were determined by multinuclear NMR techniques including 1H-13C HETCOR spectroscopy.