Organic chemistry: Natural polarity inverted.

Abstract

The concept of umpolung describes the reversal of the naturally occurring electrostatic polarization of chemical groups. It has now been used to make single mirror-image isomers of nitrogen-containing molecules. See Letter p.445 Imines, carbon–nitrogen double bonds, act as electrophiles towards carbon nucleophiles in the synthesis of amines, but the range of synthesizable amines could be greatly extended if the carbon atom of the imine could be rendered electron-rich to allow it to act as a nucleophile towards a carbon electrophile. Li Deng and colleagues have developed a procedure that achieves just that. They report the discovery and development of new chiral phase transfer catalysts that promote highly efficient asymmetric reactions of imines and enals. The reaction provides a conceptually new and practical approach towards the synthesis of chiral amino compounds.