Angewandte Chemie International Edition ( IF 12.102 ) Pub Date : 2017-12-28 , DOI: 10.1002/anie.201711363 Noriyoshi Arai, Takanori Namba, Kei Kawaguchi, Yuki Matsumoto, Takeshi Ohkuma
The asymmetric hydrogenation of aromatic γ- and δ-keto esters into optically active hydroxy esters or diols under the catalysis of a novel DIPSkewphos/3-AMIQ–RuII complex was studied. Under the optimized conditions (8 atm H2 , Ru complex/t-C4H9OK=1:3.5, 25 °C) the γ- and δ-hydroxy esters (including γ-lactones) were obtained quantitatively with 97–99 % ee. When the reaction was conducted under somewhat harsh conditions (20 atm H2 , [t-C4H9OK]=50 mm, 40 °C), the 1,4- and 1,5-diols were obtained predominantly with 95–99 % ee. The reactivity of the ester group was notably dependent on the length of the carbon spacer between the two carbonyl moieties of the substrate. The reaction of β- and ϵ-keto esters selectively afforded the hydroxy esters regardless of the reaction conditions. This catalyst system was applied to the enantioselective and regioselective (for one of the two ester groups) hydrogenation of a γ-ϵ-diketo diester into a trihydroxy ester.
A conditional promise: Chemoselectivity in the asymmetric hydrogenation of γ- and δ-keto esters into the corresponding hydroxy esters/lactones or diols under the catalysis of a novel RuII complex was precisely controlled by changing the reaction conditions (see scheme). The enantiomeric purity of both products was very high (95–99 % ee). β- and ϵ-keto esters were selectively converted into the hydroxy esters regardless of the reaction conditions.