Modified Amino Acid‐Derived Phosphine‐Imine Ligands for Palladium‐Catalyzed Asymmetric Arylation of Cyclic N‐Sulfonyl Imines

Abstract

A series of chiral phosphine‐imine ligands were synthesized starting with α‐amino acids and examined for palladium‐catalyzed asymmetric addition of arylboronic acids to cyclic N‐sulfonyl imines. High catalytic activities (up to 99% yield) and high enantioselectivities (up to 98% ee) were achieved for cyclic N‐sulfonyl aldimines and ketimines with five and six‐membered ring structures.magnified image

Chiral Brønsted Acid Catalyzed Enantioselective aza-Friedel–Crafts Reaction of Cyclic α-Diaryl N-Acyl Imines with Indoles

“…Nishimura and Hayashi developed rhodium-catalyzed asymmetric Friedel–Crafts additions to N (sulfonyl)-imines and N (acyl)-imines, resulting in α-(triaryl)-substituted methanamines. Nishimura expanded this protocol to iridium-catalyzed arylations of N (acyl)-ketimines, while Hayashi successfully employed modified amino acid derived phosphine-imine ligands for palladium-catalyzed asymmetric arylations of N (sulfonyl)-imines . Along with the aforementioned aza-Friedel–Crafts reaction described by Wang and Zhou, various organocatalytic transformations of 3-hydroxy­isoindolinones have also been developed.…”

Palladium‐Catalyzed Highly Enantioselective Arylation of Cyclic N‐Sulfonyl α‐Ketimino Esters towards the Synthesis of α‐Quaternary Chiral Amino Acid Derivatives

“…These results clearly indicate that the current Rh/diene catalyst system is sensitive to electronic and steric properties of substrates and not ideal for less reactive arylboronic acids. Inspired by earlier success of palladium‐catalyzed asymmetric addition to cyclic N ‐sulfonyl imines, we turned our attention to palladium catalyst for expanding the substrate scope. When chiral palladium‐phosphinooxazoline L4 complex was used as catalyst with AgBF 4 as additive, we were very pleased to find that the reaction with less reactive 3‐fluorophenylboronic acid could proceed smoothly and gave nearly optically pure addition product 3 h in 94 % yield (entry 8).…”

Pd‐Catalyzed Asymmetric Addition of Arylboronic Acids to Pyrazolinone Ketimines

“…Exchanging Pd(TFA) 2 for Pd(OAc) 2 and PdCl 2 led to the low level of asymmetric induction (entries 12–13). Other types of ligands widely used in asymmetric addition of arylboronic acids to ketimines such as In‐Pyrox ( L 5 ) , [18] t ‐Bu‐Nicox ( L 6 ), [19] i ‐Prox ( L 7 ) [20] and Phosphine‐imine ( L 8 ) [21] were also tested, and all of them did not show any improvement on the rection yields and enantioselectivities by using DCE as the reaction media (entries 14–17). The results were still unsatisfactory even when the reactions were conducted under previously reported reaction conditions (entries 19–20) [18,19] …”