New data on the effect of steric constraints on the chiral induction in the Orito reaction: Hydrogenation of activated steroid ketones

• Published in: Journal of molecular catalysis. A, Chemical Vol. 294; no. 1; pp. 14 - 19
• Main Authors: Szőri, Kornél, Balázsik, Katalin, Felföldi, Károly, Bucsi, Imre, Cserényi, Szabolcs, Szöllősi, György, Vass, Elemér, Hollósi, Miklós, Bartók, Mihály
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.10.2008; Elsevier
• Subjects: Catalysis; Chemistry; Cinchona alkaloids; Diastereoselective hydrogenation; Exact sciences and technology; General and physical chemistry; Platinum–alumina; Steric constraints; Steroids; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; VDC spectroscopy; Platinum–alumina; VDC spectroscopy; Cinchona alkaloids; Diastereoselective hydrogenation; Steric constraints; Steroids; Steroid; Binary compound; Cinchona; Enantioselectivity; Constraint; Chiral compound; Hydrogenation; Supported catalyst; Alkaloid; Platinum; Dicotyledones; Angiospermae; Rubiaceae; Platinum-alumina; Modified material; Transition metal; Ketone; Heterogeneous catalysis; Spermatophyta; Ketoester; Alumina
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2008.07.002

After optimization of the experimental conditions, the Orito reaction may be rendered suitable for the asymmetric hydrogenation of activated steroid ketones. ▪ Hydrogenation of α-ketoesters containing steroid groups at the ester side and at the keto carbonyl function of substrates was investigated the first time on Pt–alumina–cinchona alkaloids chiral catalysts using mild experimental conditions (room temperature, 1 bar hydrogen pressure, modifier concentration 1 mM) in the presence of acetic acid. Catalysts modified by cinchona alkaloids ensured enantioselective hydrogenation with 10–70% ee, depending on the steric structure of the substrate. In the absence of cinchonas racemic hydrogenation takes place, i.e. the chiral centers of the substrates do not participate in chiral induction. Experimental data so far obtained support the assumption that under stereochemical conditions not inhibiting adsorption of the substrate and after optimization of the experimental conditions, the Orito reaction may be rendered suitable for the asymmetric hydrogenation of bulky activated ketones. These results also supply additional evidence for the determinant role of the H-bonded adsorbed intermediate, the 1:1 complex of cinchona alkaloid and substrate in chiral induction under protic conditions.