Mechanism of the Michael addition catalyzed by bifunctional Ru catalysts

1 Mechanism of the Michael addition catalyzed by bifunctional Ru catalysts 

Recently, the mechanism of enantioselective Michael addition of malonic esters and keto esters to cyclic conjugated enones catalyzed by Ru bifunctional complexes 1 was studied in detail.  

In the case of the malonate 2, the C-boimd complexes 4a,c formed almost exclusively, whereas the reaction with the P-keto ester 3 gave complicated equilibria of numerous species. The computations showed that 

Further computational studies showed that although the C-boimd complexes 4, 5 are incapable of activating a substrate, the O-boimd complexes 6, 7 contain a 3D cavity suitable for accommodating a molecule of cyclopentenone (8). However, the computed pathways for enantioselec-tive C-C bond formation starting from 6, 7 were characterized by unreasonably high activation barriers.  

Flence, although the asymmetric environment of the Ru catalyst is efficient enough for discriminating the R- and S-pathways within a single mechanism almost perfectly, the interference of another possible way of the substrate activation reduces the overall optical yield of the catalytic reaction.  

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