Aerobic oxidation/metal-free cyclization cascades of nitrosoarenes and allenynes with TEMPO/O2: a switch of diradical to single radical intermediates

Abstract

New cascade oxidative cyclizations between nitrosoarenes and allenynes in the presence of TEMPO/O₂ mixtures afford new indanones fused with an aziridine ring. These four-component reactions are catalyst- and additive-free, yielding no byproducts with nearly 100% atom economy. Our DFT calculations indicate that the nitrosoarene/allenyne mixtures generate diradical intermediates that are intercepted by a TEMPO radical to form a single nitroxy radical to take up one O₂ molecule. This reaction model can also rationalize new chemoselectivity for nitrosoarenes bearing para-alkyl substituents.