Stereoselective reactions, catalysis

Keller, H. J., and Soos,-Z. G. Solid Charge-Transfer Complexes of Phenazines. 127, 169-216 (1985). Kellogg, R. M. Bioorganic Modelling — Stereoselective Reactions with Chiral Neutral Ligand Complexes as Model Systems for Enzyme Catalysis. 101, 111-145 (1982). 

Bioorganic modelling. Stereoselective reactions with chiral neutral ligand complexes as model systems for enzyme catalysis. R. M. Kellogg, Top. Curr. Chem., 1982,101,111-145 (93). 

Figure 10.41 Natural aldol reaction catalyzed by RibA, acceptance of nonnatural aldol donors, and azasugar precursors prepared by stereoselective RibA catalysis.

Kellogg, R. M. Bioorganic Modelling — Stereoselective Reactions with Chiral Neutral Ligand Complexes as Model Systems for Enzyme Catalysis. 101, 111-145 (1982). 

The ligand acceleration is particularly useful in catalysis with chiral ligands. Here, this phenomenon helps a stereoselective reaction mode to dominate over competing unselective pathways, leading to a highly efficient asymmetric catalysis. 

Stereoselective formation of carbon carbon and carbon heteroatom bonds remains an important goal in synthetic chemistry. Very recently lanthanide alkoxides were successfully utilized in enantioselective C-C bond forming reactions. Catalysis of aldol, cyanosilylation, nitroaldol and Michael reactions has been ascribed to the basic character of lanthanide alkoxides [158, 250, 251]. Ln3(OfBu)9 was successfully employed in test runs and subsequently optically active bidentate ligands were used (Fig. 35) [250a]. 

There are clearly some interesting observations reported in the above papers1217 that seem to pervade stereoselective reactions. First of all, the nature of the solvent in homogeneous stereoselective reactions is critical. Secondly, unique steric requirements for reactants on solid surfaces appear to lead to enhanced stereoselectivity. Thirdly, modifiers and promoters in both solution phase and solid phase catalysis appear to have marked effects on product selectivity. 

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