Chemistry

Resolving More with Less

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Science  02 Feb 2007:
Vol. 315, Issue 5812, pp. 575
DOI: 10.1126/science.315.5812.575b

Appending homogeneous catalysts to an oligomeric or dendritic support can concentrate active sites close to one another and thereby enhance the efficiency of cooperative processes. This approach has shown particular promise with the cobalt(III)-salen-catalyzed hydrolytic kinetic resolution of chiral epoxides, a highly selective reaction of interest because of the versatility of epoxides as precursors to pharmaceutically important targets. Mechanistic studies have indicated that two metal centers act cooperatively in this system, and catalysts with multiple Co-salen centers assembled as part of the backbone of a cyclic symmetrical oligomer have proven effective. Zheng et al. extend this strategy by preparing salen ligands substituted with cyclooctene and then using Ru-catalyzed ring-expanding olefin metathesis to create macrocycles with Co-salen moieties as pendant groups. The resulting compounds catalyze highly selective resolution of a range of alkyl- and aryl-substituted chiral epoxides at Co loadings as low as 0.01 mol %. The authors attribute the efficiency of this system to the spatial flexibility of the tethered metal centers. — PDS

J. Am. Chem. Soc. 129, 10.1021/ja0641406 (2007).

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