The Synthesis of (Z)-Trisubstituted Allylic Alcohols by the Selective 1,4-Hydrogenation of Dienol Esters: Improved Synthesis of (-)-[beta]-Santalol

(E)-Trisubstituted allylic alcohols are commonly prepared from the corresponding (E)-enals, themselves readily accessible by a simple aldol condensation reaction. We demonstrate that these very same (E)-enals can be converted into (Z)-trisubstituted allylic acetates (and thus alcohols) by a ruthenium-catalyzed 1,4-hydrogenation of the corresponding dienol acetates. This simple solution to a long-lasting problem was applied to an industrially feasible synthesis of (-)-[beta]-santalol.