Ketimines asymmetric hydrogenation

Iridium-Catalyzed Asymmetric Hydrogenation of Olefins with Chiral N,P and C,N Ligands 71 Table 18 Asymmetric hydrogenation of acetophenone based A-aryl ketimines... 

The presence of a heteroatom directly connected to the nitrogen atom of the imine activates it toward hydrogenation, while creating a second coordination site for the catalyst. Indeed, some successful results have been achieved for the hydrogenation of N-acylhydrazone, sulfonimide, and N-diphenylphosphinyl ketimines. The Et-DuPhos-Rh complex is an efficient catalyst for the asymmetric hydrogenation of a variety of N-acyl- ... 

Keywords Asymmetric hydrogenation, Asymmetric transfer hydrogenation, Ketimines, Oxime, Nitrones... 

No new literature data are available for the asymmetric hydrogenation of ketimines without any other functionality. 

In addition, Ir-complexes of DIFLUORPHOS (81) have been used in the asymmetric hydrogenation of quinolines (07SL2743). Very recently, its Cu(I)-complex (as CuOAc-DIFLOURPHOS) was identified as the catalyst of choice for the asymmetric reductive Mannich reaction of ketimines (93a-c) with a broad substrate scope providing high enantio- and diastereoselectivities (Scheme 19, 08JA16146). 

The asyininetric hydrogenation of imines provides an efficient and direct route for the synthesis of chiral amines. Zhu et al. [27a] reported a highly efficient asymmetric hydrogenation of acyclic A -aryl ketimines catalyzed by lr-(5 5)-25a under ambient pressure with excellent enantioselectivities (up to 91% ee) (Scheme 24). The high rigidity and bulkiness of the ligands 25 efficiently prevents the trimerization of the catalysts Ir-25 and maintains the stability of the catalysts under hydrogen atmosphere. 

The first example of an asymmetric reduction of C=N bonds proceeding via DKR was reported in 2005 by Lassaletta et al. In this process, the transfer hydrogenation of 2-substituted bicyclic and monocyclic ketimines could be accomplished via DKR by using a HCO2H/TEA mixture as the hydrogen source and a chiral ruthenium complex including TsDPEN ligand,... 

More recently, an important chiral titanium catalyst for the asymmetric reduction with hydrogen of /V-substi luted dialkyl ketimines to enantioenriched amines has been... 

All effective catalysts for the asymmetric reduction of prochiral C=N groups are based on complexes of rhodium, iridium, ruthenium, and titanium. Whereas in early investigations (before 1984) emphasis was on Rh and Ru catalysts, most recent efforts were devoted to Ir and Ti catalysts. In contrast to the noble metal catalysts which are classical coordination complexes, Buchwald s a sa-titanocene catalyst for the enantioselective hydrogenation of ketimines represents a new type of hydrogenation catalyst [6]. In this chapter important results and characteristics of effective enantioselective catalysts and are summarized. 

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