Regiodivergent Carbene/Alkyne Metathesis in Chromium-Mediated Coupling and Cyclization with 1,6-Enynes

Regiodivergent carbene/alkyne metathesis for the selective synthesis of 2-alkylidenebicyclo[4.1.0]heptanes and 1-alkenylbicyclo[3.1.0]hexanes from common 1,6-enynes precursors was demonstrated. The cyclization mode could be switched by simple addition of diamine ligands to control the relative orientation of the approaching chromium Schrock carbene equivalents generated in situ from gem-dichromiomethanes toward triple bonds. Enyne metathesis is a straightforward method for constructing complex molecules via unsymmetrical difunctionalization of carbon–carbon unsaturated bonds. However, control of the cyclization mode has been challenging. A model study based on the regiodivergent carbene/alkyne metathesis was conducted, and it determined that the reactivity of Schrock-type chromium carbene equivalents generated in situ from gem-dichromiomethanes could be well-controlled by the simple addition of diamine ligands.