A novel atom-transfer cyclisation catalysed by indium metal in halogenated solvents

Treatment of tethered alkyne–allyl halides 1a–d with indium metal in halogenated solvents affords carbocyclic vinyl halides (3a–d) via a novel atom-transfer reaction. The reactions are operationally facile and proceed smoothly at room temperature even with sub-stoichiometric quantities of the metal. Use of a halogenated solvent containing a different halide than that contained in the substrate affords a mixture of products arising from intramolecular halide transfer and abstraction of a halide atom from solvent.