Cyclopropanation–ring Expansion of 3-Chloroindoles with Α-Halodiazoacetates: Novel Synthesis of 4-Quinolone-3-carboxylic Acid and Norfloxacin

We present a short and efficient way of synthesizing two synthetically versatile 4-quinolone-3-carboxylate building blocks by cyclopropanation-ring expansion of 3-chloroindoles with α-halodiazoacetates as the key step. This novel transformation was applied towards the synthesis of the antibiotic drug norfloxacin.