Managing highly coordinative substrates in asymmetric catalysis: A catalytic asymmetric amination with a lanthanum-based ternary catalyst

Full details of a catalytic asymmetric amination with a lanthanum/amide-based ligand catalyst system are described. A catalyst comprising La(NO₃)₃·6H₂O, (R)-3a and H-D-Val-O^tBu was identified to promote the catalytic asymmetric amination of nonprotected succinimide derivative 1 with as little as 1 mol % catalyst loading. Mechanistic studies by various spectroscopic analyses and several control and kinetic experiments suggested that the catalyst components were in equilibrium between the associated and dissociated forms, and that the reaction likely proceeded through a La(NO₃)₃· 6H₂O/(R)-3a/H-D-Val-O^tBu ternary complex. This catalyst system was also effective for asymmetric amination of N-nonsubstituted α-alkoxycarbonyl amides 7, hitherto unprecedented substrates in asymmetric catalysis, probably due to their attenuated reactivity and difficult stereocontrol, affording the amination products in up to >99% yield and >99% ee. The high catalytic performance and enantiocontrol of the reaction with highly coordinative substrates were achieved by the activation/recognition of the substrates exerted by coordination to lanthanum and hydrogen bonding cooperatively in the transition state.