Aldehyde Addition to 1,3-Butadiyne-Derived Zirconacyclocumulenes: Stereoselective Synthesis of <i>cis</i>-[3]Cumulenols

The direct addition of aldehydes to zirconacyclocumulenes generated through the coupling reactions of benzynezirconocenes with 1,3-butadiynes is achieved cleanly under controlled reaction conditions, which provids a highly stereoselective method for the synthesis of tetra-substituted [3]cumulenols. DFT calculations suggest that there is an equilibrium between seven-membered zirconacyclocumulene (3) and the less stable but more reactive five-membered α-alkynylzirconaindene (2) in the process. The aldehyde reacts with the five-membered zirconaindene intermediate through a cyclic SE2′ pathway to afford cumulenol products after hydrolysis.