Fast Transition Metal‐Free Synthesis of Functionalized Oxindoles and Dihydroquinoline‐2‐ones Under Microwave Irradiation

A fast transition metal-free and synthetic methodology for generating a broad scope of highly functionalized oxindoles and dihydroquinolin-2-ones was developed. The exploitation of formamide or N-methylformamide (reagent/solvent) and potassium persulfate (radical initiator) under microwave irradiation resulted in a fast radical reaction of 10 s. The functionalized oxindoles and dihydroquinoline-2-ones allowed us to readily access several spirocompounds such as spiro[oxindole-gamma-lactones], spiro[oxindole-delta-lactones], spiro[dihydroquinoline-2-one-gamma-lactones], spiro[oxindole-imides] and spiro[dihydroquinoline-2-one-imides].