Synthesis of 5‐methyl‐4‐oxo‐quinolinecarboxylic acids

A series of 5‐methyl‐4‐oxo‐3‐quinolinecarboxylic acids was prepared in which the eight‐position was substituted with fluorine, chlorine, methyl, or hydrogen. These quinolones were synthesized from the appropriate 2‐methyl‐3,4,6‐trifluorobenzoic acids which were derived from oxazolines 8 and 16 . The oxazoline moiety served as both an ortho ‐director (where feasible) and a protecting group; a trimethylsilyl moiety was used to block the most acidic site in the molecule.