Science 327, 986–990 (2010)

The products of chemical reactions often have different spatial arrangements, or stereoisomers, of which only one is useful (as a drug, for example). As a result, many chemists are focused on controlling such reactions to select only the desired product.

Eric Jacobsen and his colleagues at Harvard University in Cambridge, Massachusetts, have developed one such strategy involving two cooperating catalysts. They first use an acid catalyst to transform a molecule's nitrogen-based imide group into a reactive iminium ion. A second catalyst then cradles this ion through a network of weak intermolecular attractions — much like the way that biological enzymes position their substrates. This ensures that one reaction orientation is favoured, meaning that only one stereoisomer is formed. The reaction is 5–10 times slower than its one-catalyst variant, but highly selective.