Asymmetric hydrogenation of α-keto acid derivatives by rhodium-{amidophosphine-phosphinite} catalysts

Article abstract of DOI:10.1016/S0957-4166(97)00078-5

The enantioselective hydrogenation of several α-keto esters (3a-f, 5a-j), α-keto amides (7a-e) and isatine derivatives (9a-d) with a set of four representative neutral homogeneous rhodium-amidophosphine-phosphinite catalysts has been investigated. Trifluoroacetate-Rh-AMPP catalytic precursors promoted the rapid, efficient synthesis of aliphatic α-hydroxy esters 4a-f in moderate to high enantioselectivities (66-95% eel, in contrast to most aromatic α-hydroxy esters 6a-j (8-81% eel. Best enantioselectivities for α-hydroxy amides 8a-e (85-95% eel and dioxindoIes 10a-d (80-94% eel were obtained with chloro-Rh-AMPP precursors. It is proposed that, contrary to α-keto amides, α-keto esters do not chelate onto the rhodium center and that, in such circumstances, the asymmetric induction is mainly controlled by the steric hindrance around the C=O function.