Free radical domino reactions in the synthesis of small ring compounds: multiple annulation of cyclopropane-containing polycycles

Free radical approach to fused vinylcyclopropane derivatives is described. Homolytic decomposition of Barton esters 4a–f in the presence of activated alkynes affords bicyclo〚3.1.0〛hex-2-ene derivatives 5a–g in moderate yields (18–52 %). The propagation sequence comprises: intermolecular addition/5-exo-cyclization/3-exo-cyclization/β-elimination, and allows for a one-pot synthesis of bicyclic cyclopropane derivatives starting from two acyclic, unsaturated compounds.