SynPhos

The sense of diastereoselectivity in the dynamic kinetic resolution of 2-substi-tuted / -keto esters depends on the structure of the keto ester. The ruthenium catalyst with atropisomeric diphosphine ligands (binap, MeO-biphep, synphos, etc.) induced syn-products in high diastereomeric and enantiomeric selectivity in the dynamic kinetic resolution of / -keto esters with an a-amido or carbamate moiety (Table 21.21) [119-121, 123, 125-127]. In contrast to the above examples of a-amido-/ -keto esters, the TsOH or HC1 salt of /l-keto esters with an a-amino unit were hydrogenated with excellent cwti-selectivity using ruthenium-atropiso-... 

Based on hydrogenations of model substrates, several new ligands promise to have a similar potential as those described above. For example, Ru-Solphos (Solvias) catalysts have been shown to hydrogenate various yS-keto esters and / -diketones with ee-values up to >99% and TONs of up to 100000 (for ethyl-3-oxobutanoate) [75], while Ru-Synphos (Synkem) [107] catalysts achieved 99.4% ee at an SCR of 7000 for the hydrogenation of ethyl acetoacetate (for ligand structures, see Fig. 37.28). 

SYNPHOS AND DIFLUORPHOS AS LIGANDS FOR RUTHENIUM-CATALYZED HYDROGENATION OF ALKENES AND KETONES... 

Ruthenium(II) complexes bearing atropisomeric diphosphine ligands have proved to be efficient systems for the hydrogenation of a wide range of prochiral substrates. A new catalytic system has been developed based on ruthenium complexes having SYNPHOS and DIFLUORPHOS as chiral diphosphanes (Figure 3.6). 

SYNTHESIS OF IN SITU GENERATED [RuBr2((5)-SYNPHOS)] AND [RuBr2((S)-DIFLUORPHOS)]... 

Table 3.7 Asymmetric ruthenium-catalyzed hydrogenations using SYNPHOS-Ru(II) and DIFLUORPHOS-Ru(II) catalysts.

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