Secondary Cationic Interaction Driven Substrate Ligand Affinity for Pd(II)-Catalyzed Enantioselective C-H Activation of Ferrocenyl Amines

Secondary amines as a directing group for C-H activation have limitations as they are prone to undergo oxidation, allylic deamination, and β-hydride elimination. The fundamental challenge observed here is the competition between the desired C-H activation versus the vulnerable β-C-H bond of secondary amine when the substrate ligand affinity is not strong enough. Herein, a potential of axially chiral NOBINAc ligand is revealed on accelerating enantioselective Pd(II)-catalyzed C-H activation process of ferrocenyl secondary amines. Further, the secondary interaction of cesium cation with NOBINAc ligand and sulfonate group of secondary amine plays an impressive role in mitigating the potential threat of β-hydride elimination via an enhanced substrate ligand affinity. This approach resulted in enantioselective C-H activation and intermolecular annulation of ferrocenyl secondary amines with allenes, leading to ferrocene fused tetrahydropyridines up to 70% yields and 98% of ee.