Metal- and base-free spirocyclization of alkylidene oxindoles via photo- and mechanochemically-generated nitrile ylides and nitrile imines as 1,3-dipoles

Abstract

Herein we have reported an expedient synthesis of spiro[pyrrolidine-3,3′-oxindole] and 2′-aryl-2′,4′-dihydrospiro[indoline-3,3′-pyrazol]-2-one under metal- and base-free conditions through the 3 + 2 cycloaddition reactions of in situ generated nitrile ylides and nitrile imines with alkylidene oxindoles in good to excellent yields. The nitrile ylides are generated through acetonitrile insertion onto carbenes generated from blue LED irradiation of aryl diazo esters. The nitrile imines were formed under mechanochemical conditions from diazo esters and aryl diazonium tetrafluoroborates.