The construction of all-carbon quaternary centers, especially those containing an alkyne-substituted framework, represents an important challenge in organic synthesis. Here we present a novel Fe-catalyzed selective formal insertion of diazo compounds into C(sp)−C(sp 3 ) bonds of propargyl alcohols under mild conditions that enables the streamlined construction of alkynesubstituted all-carbon quaternary centers. This unique strategy starts with in situ generation of an ester group in the presence of carboxylic acids, followed by insertion of metal-carbene into C(sp)− C(sp 3 ) bonds, which may open up a new reaction mode for exploring metal-carbene insertion into acyclic C−C bonds.

The radical tandem bicyclization provides a novel approach for the preparation of complex polycyclic compounds in synthetic chemistry. Herein, we first described a tandem radical bicyclization reaction of CN-containing 1,6-enynes...