SEQUENTIAL CYCLIZATION SILYLATION OF DIENYNES CATALYZED BY AN ORGANOYTTRIUM COMPLEX/

The organoyttrium complex Cp2YCH3. THF (Cp* = C5Me5) has been shown t o be an effective precatalyst for the selective sequential cyclization /silylation of dienynes. The catalyst's ability to insert the alkyne i n preference to the alkenes in a regioselective manner, combined with the high diastereoselectivity of the intramolecular insertion process, leads to bicyclo[3.3.0]octane products in high yield. The stereochemi stry of the exocyclic olefin, the ring fusion, and the ring substituen ts are all controlled in the reaction. The cyclization of dienynes thu s affords silylated carbobicyclics with high diastereoselectivities in excellent yields.