Nucleophilic addition to a p-benzyne derived from an enediyne:: A new mechanism for halide incorporation into biomolecules

Biosynthesis of haloaromatics ordinarily occurs by electrophilic attack of an activated halogen species on an electron-rich aromatic ring. We now present the discovery of a new reaction whereby a nucleophilic halide anion can be attached even to an aromatic ring without activating substituents. We show that the enediyne cyclodeca-1,5-diyn-3-ene, in the presence of lithium halide and a weak acid, is converted to 1-halotetrahydronaphthalene. The kinetics are consistent with rate-limiting cyclization to a p-benzyne biradical that rapidly adds halide and is then protonated. This reaction has interesting mechanistic features and important implications for incorporation of halide into biomolecules.