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.