Researchers have developed a new reaction to produce chlorinated compounds with high isomeric purity. Such compounds are important building blocks for target molecules. However the molecules come in left- and right-handed versions (enantiomers). They can be produced from carboxylic acids, by replacing an acid with a chlorine; however, conventional methods produce equal mixtures of both isomers, but the new method with a chiral amine catalyst specifically yields the desired isomer.