Pyridine‐Boryl Radical‐Catalyzed [3 + 2] Cycloadditions of Alkyne‐Tethered Cyclopropyl Ketones

Bicyclo[3.3.0]octanes represent crucial structural motifs found in various bioactive natural compounds. In this study, we present the first metal‐free formal [3 + 2] cycloadditions of alkyne‐tethered cyclopropyl ketones via pyridine‐boryl radical catalysis, affording bicyclo[3.3.0]octanes with high efficiency and broad substrate scope. This reaction features the generation of ketyl radical by pyridine‐boryl radical and a consecutive 5‐exo‐dig and 5‐exo‐trig radical cascade process.