Ruthenium pyridinebisoxazoline

In another protocol using a ruthenium(pyridinebisoxazoline)(pyridinedicarboxylic acid) catalyst 26 and iodosylbenzene as the terminal oxidant, Seller and co-workers <03TL7479> found that the addition of water and protic solvents resulted in a 100-fold acceleration of the epoxidation, presumably due to a ligand dissociation effect that promotes the oxidation of the ruthenium catalyst. Thus, the conversion of rrans-stilbene 27 to the corresponding 5,S-epoxide 28 required 96 h in anhydrous toluene, but only 1 h in the presence of r-butanol and water. The enantioselectivity of the reaction was not significantly affected (63% and 57% ee, respectively). 

Whilst the Sharpless epoxidation with titanium catalysts and the Jacobsen-Katsuki epoxidation with manganese(salen) complexes are at the forefront of enantioselec-tive epoxidation with metal catalysts, there are alternative systems available. Ruthenium pyridinebisoxazoline (PYBOX) complexes have been independently reported, using either phenyliodinium diacetate or sodium periodate as... 

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