PerspectiveChemistry

Heat and Light Switch a Chiral Catalyst and Its Products

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Science  18 Mar 2011:
Vol. 331, Issue 6023, pp. 1395-1396
DOI: 10.1126/science.1203272

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Summary

A right-handed glove won't fit a left hand because our hands are chiral. They are mirror images of each other, but despite this symmetry, their shapes cannot be superimposed one on the other. Molecules that are nonidentical mirror images are called enantiomers. Most biomolecules are found only as one of the two enantiomeric forms, and drug molecules that interact with biomolecular targets are usually more active in pure enantiomeric form. Chiral molecules can be prepared from the readily available, achiral starting materials, and many reactions that favor one chiral product (asymmetric reactions) do so by using a catalyst that itself is chiral (1). However, a versatile method must be able to make both left- and right-handed products, which usually requires having to make both enantiomers of the catalyst. On page 1429 of this issue, Wang and Feringa (2) introduce a conceptually new approach in which the structure of a single catalyst can be manipulated by cycles of light and heat to pulses. These processes drive internal rotation around a carbon-carbon double bond and create two forms of the catalysts that give reaction products of opposite chirality (3).