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Bicyclo3.3.0octanes 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 bicyclo3.3.0octanes 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.
Hua et al. (Fri,) studied this question.