title: Ruthenium-catalyzed asymmetric hydrogenation of 3-oxoglutaric acid derivatives: a study of unconventional solvent and substituent effects.
abstract: A series of 3-oxoglutaric acid derivatives have been hydrogenated in different solvents in the presence of [RuCl(benzene)(S)-SunPhos]Cl (SunPhos = (2,2,2',2'-tetramethyl-[4,4'-bibenzo[d][1,3]dioxole]-5,5'-diyl)bis(diphenylphosphine)). Unlike simple β-keto acid derivatives, these advanced analogues can be readily hydrogenated in uncommon solvents such as THF, CH(2)Cl(2), acetone, and dioxane with high enantioselectivities. Two possible catalytic cycles have been proposed to explain the different reactivities of these 1,3,5-tricarbonyl substrates in the tested solvents. The C-2 and C-4 substituents had notable but irregular influence on the reactivity and enantioselectivity of the reactions. More pronounced solvent effects were observed: the ee values increased from around 20% in EtOH or THF to 90% in acetone. Inversion of the product configuration was observed when the solvent was changed from EtOH to THF or acetone, and a mixed solvent system can lead to better enantioselectivity than a single solvent.
authors.affiliation: School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, PR China.
authors.forename: Wanfang
authors.initials: W
authors.lastname: Li
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Tao
authors.forename: Xin
authors.initials: X
authors.lastname: Ma
authors.forename: Weizheng
authors.initials: W
authors.lastname: Fan
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Li
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Zhao
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Xie
authors.forename: Zhaoguo
authors.initials: Z
authors.lastname: Zhang