Switching Hands

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Science  25 May 2012:
Vol. 336, Issue 6084, pp. 962
DOI: 10.1126/science.336.6084.962-c

Most stereoselective catalysts are designed to form just one stereoisomeric product, but there is increasing interest in catalysts that could switch the sense of the desired product through some external stimulus. Mortezaei et al. observed that the helical arrangement of two quinoline moieties in a particular polydentate ligand coordinated to copper varied depending on the metal's oxidation state. The ligand binds through the N atoms of the quinoline groups and either an O atom of a tethered methionine derivative for Cu(II) complexes or the S atom of the side chain for Cu(I) complexes. The authors went on to synthesize derivatives of these complexes in which the quinolines bear catalytic urea groups, so as to exploit the redox-driven conformational switching in control of product stereochemistry. They show that the Michael addition of diethyl malonate to trans-β-nitrostyrene occurs with ∼70% enantiomeric excess for the S and R products with the Cu(II) and Cu(I) catalysts, respectively, in acetonitrile and in the presence of base.

J. Am. Chem. Soc. 134, 10.1021/ja302283s (2012).

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