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

Abstract 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 CF 3 CHCHCO 2 Et, 3,3,3-trifluoro 1-(phenylsulfonyl)-1-propene CF 3 CHCHSO 2 Ph and 2-(trifluoromethyl) propenoic acid CF 3 (HO 2 C)CCH 2 ] gave several trifluoromethyl-substituted pyridine systems in moderate yield (20–56%). Their structures were determined by multinuclear NMR techniques including 1 H- 13 C HETCOR spectroscopy.