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.