Iron‐Catalyzed Borylation of Propargylic Acetates for the Synthesis of Multisubstituted Allenylboronates

A novel iron‐catalyzed borylation of propargylic acetates leading to allenylboronates has been developed. The method allows the preparation of a variety of di‐, tri‐ and tetrasubstituted allenylboronates at room temperature with good functional group compatibility. Stereochemical studies show that an anti‐S(N)2’ displacement of acetate by boron occurs; this also allows transfer of chirality to yield enantiomerically enriched allenylboronates. The synthetic utility of this protocol was further substantiated by transformations of the obtained allenylboronates including oxidation and propargylation.