A novel and efficient synthesis of 3-carboxy-4-oxo-1,8-naphthyridines using magnesium chloride

A novel and efficient synthesis of 5-oxo-6-carboxy-naphthyridines is reported in this Letter along with a discussion of scope and limitations. Activated 3-nicotinic acids readily acylate the magnesium anion of 2-(benzothiazol-2-yl) or 2-(benzimidazol-2-yl) acetates. The corresponding product can then undergo cyclization spontaneously or under very mild conditions to give the desired naphthyridine products. Only near stoichiometric ratios of reactants are required for this approach and the products are isolated in pure form after a trituration making this an efficient process.