Fe-Catalyzed Selective Formal Insertion of Diazo Compounds into C(sp)-C(sp 3 ) Bonds of Propargyl Alcohols: Access to Alkyne-Substituted All-Carbon Quaternary Centers.

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 alkyne-substituted 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.