A facile synthetic route to 2-trifluoromethyl-substituted polyfunctionalized chromenes and chromones

A method for the preparation of methyl 4-hydroxy-2-(trifluoromethyl)-4H- chromenes-3-carboxylate derivatives 3a-j from readily available trifluoromethylated building block methyl (Z)-2-bromo-4,4,4-trifluoro-2- butenoate 1 was described. Treatment of 3a-j with Sarrett reagent in CH ₂Cl₂ generated methyl 4-oxo-2-(trifluoromethyl)-chromene- 3-carboxylate derivatives 4a-h with moderate to good yields, which can be converted to 2-trifluoromethyl-substituted multifunctional benzoxepins through cyclopropanation and Lewis acid-catalyzed ring opening.