Cobalt(II)-Catalyzed Aerobic Oxidation of Terminal-Capped Alkynyl α‑Cyano Alkanone Systems. An Oxygen-Mediated Radical Chain Reaction

A new N-hydroxyphthalimide
(NHPI)/Co­(II)-catalyzed
protocol, mechanistically involving a sequence of α-hydrogen
abstraction, 5-exo-dig cyclization,
oxygen capture, hydrogen transfer, and 1,4-dehydration, has been developed
to facilitate aerobic oxidation of aryl-, silyl-, and alkyl-capped
alkynyl α-cyano alkanone systems to the corresponding highly
functionalized products in an effective manner, thus turning this
novel chain reaction, originally occurring spontaneously in low yields,
into a practical methodology.