Photoinduced Copper-Catalyzed Radical Cascade Sonogashira-Type Coupling of Unsaturated Oxime Esters with Alkynes

A photoinduced copper-catalyzed radical cascade Sonogashira-type coupling of unsaturated oxime esters with terminal alkynes has been developed. The transformation proceeds under redox-neutral conditions via single-electron transfer (SET) from photoexcited Cu(I) acetylides, generating iminyl radicals that undergo cyclization followed by alkynylation. This strategy enables efficient construction of alkynylated N-heterocycles from readily available substrates, featuring mild conditions, broad scope, and full suppression of competing N-alkynylation. Mechanistic studies support a Cu(I)/Cu(II)/Cu(III) cycle involving photoinduced SET and radical cyclization, highlighting Cu-acetylide complexes as photoreductants in radical relay processes.