ChemInform Abstract: Unprecedented Halide Dependence on Catalytic Asymmetric Hydrogenation of 2‐Aryl‐ and 2‐Alkyl‐Substituted Quinolinium Salts by Using Ir Complexes with Difluorphos and Halide Ligands.

Abstract

Halide Ligands. -An unexpected superiority of the axially chiral chloro-and bromo-iridium complexes (I) over the corresponding iodo-complex as catalysts for the title reaction of 2-aryl-and 2-alkylquinolinium halides is observed. The method is applied as key step for the synthesis of bioactive compound (X).

Catalysis, kinetics and mechanisms of organo-iridium enantioselective hydrogenation-reduction

“…One of the representative examples in this class is the exceptional cationic dinuclear IrIJIII) complex 75. 64,65 The substrate scope features excellent hydrogenation of 2-aryl substituted quinolines and 2-alkyl and 2-aryl quinoxalines. Additionally, complex 75 has also proved to be formidable in the reduction of 1-or 3-substituted isoquinolinium salts.…”

Enantioselective Synthesis of Alcohols and Amines by Iridium‐Catalyzed Hydrogenation, Transfer Hydrogenation, and Related Processes

“…[78] A catalyst loading of 0.02 mol % afforded ee values up to 93 %. Similarly, replacement of the phenyl groups on phosphorus in (R)-SegPhos (45) with DTBM groups led to a more efficient catalyst (47) that could be used with catalyst loadings as low as 0.004 mol %. Knochel, Cheemala, and co-workers used chiral P,N-ferrocenyl ligands 79 in the Ir-catalyzed reduction of N-(3,5-dimethyl-4-methoxy)phenylalkylimines, which worked under mild reaction conditions and afforded excellent enantioselectivities (Scheme 36).…”

“…[47] The enantioselectivity is highly dependent on the dihedral angles (q) of the ligand, and the highest ee was obtained with (S)-difluorphos (49), which has the smallest angle. In contrast to other reports, [34,35] chloro and bromo-bridged complexes 48 were working better than iodo-bridged ones.…”