An unusual ruthenium-catalyzed cycloisomerization of alkynes and propargyl alcohols.
CpRu(NCCH3)3+PF6- catalyzes the cycloisomerization of diyne-ols to alpha,beta,gamma,delta-unsaturated aldehydes and ketones in good-to-excellent yields. 1-Hydroxy-2,7-diynes and 1-hydroxy-2,8-diynes can be utilized to form highly functionalized five- and six-membered rings, respectively. Tertiary as well as secondary propargyl alcohols are cycloisomerized to a single isomeric product. A wide variety of tether substitution can be tolerated. Even totally unsubstituted tethers can be employed, as geminal disubstituents are not required for cyclization. Additional hydroxyl substituents at an alternative "internal" propargylic position are eliminated during the reaction-a feature that leads to a convenient cyclopentadiene synthesis. Furthermore, 3-hydroxy-1,6-diynes also can be cyclized to form cross-conjugated aldehydes.