CHEMOSELECTIVITY IN THE RUTHENIUM-CATALYZED REDOX ISOMERIZATION OF ALLYL ALCOHOLS

Adjustment of oxidation level by internal hydrogen reorganization represents a highly efficient synthetic protocol. Cyclopentadienylbis(triphenylphosphine)ruthenium chloride in the presence of triethylammonium hexafluorophosphate catalyzes the redox isomerization of allyl alcohols to their saturated aldehydes or ketones. High chemoselectivity is observed since simple primary and secondary alcohols and isolated double bonds are not affected by this catalyst. The reaction is sensitive to the degree of substitution on the double bond and requires relatively unhindered olefins. Switching to indenylbis(triphenylphosphine)ruthenium chloride in the presence of triethylammonium hexafluorophosphate significantly expands the scope of the reaction to substrates bearing more substituted olefinic linkages and to cyclic substrates of rings containing eight or more members. The mechanism is probed by deuterium labeling, which shows that the metal catalyzes an intramolecular 1,3-hydrogen shift of the carbinol hydrogen to the terminal olefinic position.