Unusual reaction of aryldiazoacetates with enamines: highly effective synthesis of γ-ketoesters

The reaction of aryldiazoacetates with enamines catalyzed by copper and rhodium complexes provided γ-ketoesters in good yields. Careful analysis of the crude reaction mixture revealed a substituted enamine as the primary product, which was hydrolyzed over silica gel to give a γ-ketoester as the final product. A reaction mechanism involving nucleophilic addition of an enamine to a metal carbene and subsequent hydrogen transfer was proposed.