Improved Methodology for the Preparation of Chiral Amines

Cozzi et al. developed the use of phosphino oxazolines derived ligands. [23] Using 0.1 mol %
of the catalyst (catalyst 5, figure 2.4), 50 bar (725 psi) H 2 , CH 2 Cl 2 , 25 °C, 4 h, the ee was
86% with complete conversion for phenyl methyl N-aryl imine (structure 1, figure 2.3).
Ruthenium catalysts earlier developed by Noyori for ketone reduction were useful for imine
reduction which was tested by Cobley. [24] Using 1.0 mol % of RuCl 2 (diphosphine) (diamine)
(catalyst 6, figure 2.4), 15 bar (218 psi) H 2 , 100 mol % of t-BuOK in t-BuOH for in situ
activation of the catalyst, 65 °C, 20 h, the ee was 91% with complete conversion for phenyl
methyl N-aryl imine (structure 1, figure 2.3).
Grützmacher was successful in using mixed phosphane olefin ligand for imine reduction. [25]
Using 1.0 mol % of the iridium catalyst (catalyst 7, figure 2.4), 50 bar (725 psi) H 2 , CHCl 3 ,
50 °C, 2 h an ee of 86% with >98% yield for phenyl methyl N-aryl imine was reported
(structure 1, figure 2.3).
Niedercorn was able to reduce N-aryl imines with Ir-aminophosphine-oxazoline derived
catalyst. [26] Using 2.0 mol % of the catalyst (catalyst 8, figure 2.4), 20-50 bar (290-725 psi)
H 2 , CH 2 Cl 2 , 12 h an ee was 90% with full conversion for phenyl methyl N-aryl imine was
reported (structure 1, figure 2.3).
Andersson developed a new class of chiral phosphine-oxazoline ligands for iridium imine
reduction. [27] Using 0.5 mol % of the catalyst (catalyst 9, figure 2.4), 20 bar (290 psi) of H 2 ,
CH 2 Cl 2 , 25 °C over 2 h an ee was 90% with 98% conversion for phenyl, methyl N-aryl
imines (structure 1, figure 2.3). He also tested his catalyst for reducing p-fluoro phenyl
methyl N-aryl imine and reported 89% ee in 2 h, for p-OMe phenyl methyl N-aryl imine the
ee was 86% within 2-3 h, for p-chloro phenyl methyl N-aryl imine the ee was 89% within 1.5
h with full conversion. In case of o-Me phenyl methyl N-aryl imine the ee was lower (83%)
and the conversion was much lower (52%) after even 12 h (structure 3, Figure 2.3). Later
they reported 78% ee for phenyl ethyl N-aryl imines (structure 2, figure 2.3). 2-naphthyl
methyl N-aryl imine was reduced with 91% ee. [28]
Blom prepared a new class of diphenylphosphanyl sulfoximines ligands. [29] Using 1.1 mol %
of the Ir-Sulxoimine catalyst (catalyst 10, figure 2.4), 2.0 mol % of iodine, 20 bar (290 psi) of
44