Alternative Hydrogen Source for Asymmetric Transfer Hydrogenation in the Reduction of Ketones

cis-1,4-Butenediol is shown to be a highly active hydrogen source for asymmetric transfer hydrogenation in the reduction of ketones. With the use of a ruthenium catalyst, cis-1,4-butenediol is isomerised and subsequently oxidised to a lactone as an irreversible step, which provides the driving force for the asymmetric reduction of ketones.