Highly selective hydrolytic kinetic resolution of terminal epoxides catalyzed by chiral (salen)Co^III complexes. Practical synthesis of enantioenriched terminal epoxides and 1,2-diols

The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)Co^III complex 1·OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H₂O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to ≥ 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H₂O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (k_rel) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, k_rel values for the HKR exceed 50, and in several cases are well in excess of 200.