Multi-Task Catalyst: Ruthenium Hydride Catalyzed Atom-Economical Bond Forming Reactions

In this account, we focused on the high potentials of ruthenium hydride complexes, such as RuHCl(CO)(PPh3)(3), as a multi-task catalyst for atom-economical C-C bond-forming reactions. In our initial work, we discovered that the dimerization of primary unsaturated alcohols to give alpha-hydroxymethyl ketones was promoted by RuHCl(CO)(PPh3)(3). Some insights into the reaction mechanisms suggest that double bond-isomerization leading to aldehydes, transfer hydrogenation to give enals, formation of ruthenium enolates, aldol reactions of the enolates with aldehydes, and the subsequent beta-hydride elimination are involved in the unusual dimerization. Taking advantages of the ability of transfer hydrogenation by RuHCl(CO)(PPH3)(3), we developed reductive dimerization reaction of enals in the presence of secondary alcohols and cross-coupling reaction of enals with primary alcohols, both of which led to alpha-hydroxymethyl ketones. The regioselective addition of aldehydes to enones was also successful, which provides a useful entry to 2-alkyl-substituted 1,3-diketones. The ruthenium hydride-catalyzed cross-coupling reaction of dienes with aldehydes gave beta,gamma-unsaturated ketones in high yield with high regioselectivity. RuHCl(CO)(PPh3)(3) is also an efficient catalyst for lactonization of both dialdehydes and keto aldehydes. The consecutive C-C and C-O bond forming reactions were achieved using enones and dialdehydes, which gave keto lactones in good yields.