Asymmetric Hydrogenation by Relay Catalysis with FLPs and CPAs: Stereodivergent Synthesis of 3-Substituted Flavanones

Abstract

To access flavanones bearing two contiguous stereogenic centers, a metal-free asymmetric hydrogenation of racemic 3-alkylidene flavanones has been developed by relay catalysis with achiral FLPs and chiral phosphoric acids, which represents a successful detour for the challenging hydrogenation of 3-substituted flavones. A wide range of trans- and cis-flavanones were obtained in high yields and ≤97% ee.

Rhodium‐Catalyzed Asymmetric Macrocyclization towards Crown Ethers Using Hydroamination of Bis(allenes)

“…As the stereoisomers are separable, it is possible to have all the diastereomers by reaction of an unsymmetrical BA with a phenylenediamine [31] . For example, the trans ‐stereoisomers ( S , S and R , R ) of CE36 were obtained by ligand exchange and confirmed by X‐ray crystallography.…”

Asymmetric catalysis with FLPs

“…A wide range of trans - and cis -flavanones 69 and 70 were obtained with high levels of yields and ee values (Scheme 34). 44…”

Asymmetric Reduction of Quinolines: A Competition between Enantioselective Transfer Hydrogenation and Racemic Borane Catalysis

“…The combination of FLP catalysis with another well-established asymmetric catalysis might provide a promising direction to further extend the substrate scopes and acquire high ee’s with achiral Lewis acids. Aiming at this goal, recently, we developed a relay catalysis with an achiral FLP and chiral proton shuttle for the asymmetric hydrogenation of chromones . Very recently, a chiral phosphoric acid (CPA)-catalyzed ATH of benzoxazinones with regenerable dihydrophenanthridine derived from achiral borane catalysis under H 2 has been successfully explored to afford the desired products with up to 99% ee (Scheme ).…”