Oxidation of 2-and 3-halogenated quinolines: An easy access to 5-and 6-halogenopyridine-2,3-dicarboxylic acids

Pyridine-2,3-dicarboxylic acids bearing an halogen in the position alpha or beta to the nitrogen atom were synthesized by oxidation of the correspondi ng quinolines. Two methods, using either ozone followed by hydrogen peroxid e or ruthenium tetroxide under catalytic conditions were used. Diacids 1b,c and 2a-c substituted in 6-position by a chlorine or bromine and in 5-posit ion by a fluorine, chloride or bromine, respectively, were isolated in yiel ds ranging from 46-71%. Yields of 6-fluoro and 6- or 5-iodo diacids 1a,d an d 2d did not exceed 30%.