Synthesis of fused bromofurans via Mg-mediated dibromocyclopropanation of cycloalkanone-derived chalcones and Cloke-Wilson rearrangement.

A convenient two-step sequence for the conversion of alkylidenecycloalkanones to bromofurans is reported. The steps involve Mg-mediated diastereoselective dibromocyclopropanation of alkylidenecycloalkanone followed by acidic alumina-mediated regioselective ring expansion of the cyclopropyl ketone. The scope of the reaction was investigated using alkylidenecycloalkanones derived from tetralone, indanone, and benzosuberone to afford 2-aryl-3-bromofurans fused to various benzocycloalkanes. Representative examples of stereoconvergent dibromocyclopropanation and total aromatization of the furobenzocycloalkane are also reported.