Regioselectivity control in a ruthenium-catalyzed cycloisomerization of diyne-ols.

The ruthenium-catalyzed cycloisomerization of diynes containing one silyl alkyne and one propargyl alcohol yields 2-silyl-[6H]-pyrans instead of the expected unsaturated acylsilanes except when additional conjugation of a aromatic ring is present at the delta-position. Under certain conditions, a facile ruthenium-catalyzed isomerization of the product takes place as well. This regioselectivity of the cyclization can be controlled by the choice of solvent system. DFT calculations confirm the expected greater stability of the silyl-pyrans relative to the acylsilanes.