Ruthenium-catalyzed regio- and enantioselective allylic substitution with water: direct synthesis of chiral allylic alcohols.

Enantioselective allylic substitution catalyzed by transitionmetal complexes is an important process in organic synthesis. For many years, mainly palladium complexes that contain chiral ligands have been employed as efficient catalysts in these reactions. Recent studies have demonstrated that chiral catalysts based on other transition metals show different regioselectivity in the synthesis of branched allylic products via monosubstituted p-allyl intermediates. Although a variety of carbon and nitrogen nucleophiles can be used in those reactions, applicable oxygen nucleophiles are still limited to phenols and alcohols, which produce allylic ethers. Thus, enantioenriched branched allylic alcohols, which serve as useful chiral building blocks, are often synthesized by other processes, such as the hydrogenation of a,b-unsaturated ketones, the nucleophilic addition of vinylmetal reagents to aldehydes and ketones, and the kinetic resolution of racemic allylic alcohols. Recently, new ways to access these compounds have been developed, and they involve allylic substitution by a two-step conversion involving allylic esters and silyl ethers (Scheme 1; OPG= ester or silyl