Efficient Fluorination of Organic Molecules with Chiral Anions

Many pharmaceuticals and agrochemicals, as well as liquid-crystal materials, contain fluorine atoms. The introduction of the small, highly electronegative fluorine atom into an organic molecule can greatly change its physical and biological properties and, with careful design, improve its chemical and metabolic stability as well as its biological activity (1). In many cases, fluorine has been introduced on an aromatic ring or as a trifluoromethyl group, but fluorine substitution at a chiral carbon center—one that has right- or left-handed stereochemistry—is attracting increasing attention, because adding a fluorine atom to a chiral center can alter the conformation of the molecule and allow fine-tuning of its biological activities. On page 1681 of this issue, Rauniyar et al. (2) report on an efficient fluorocyclization reaction that converts achiral compounds containing double bonds into complex, chiral fluorine derivatives. A chiral anionic phase-transfer catalyst helps a normally insoluble reagent enter the organic phase and selectively add fluorine to a carbon atom.