Bridged synthons from tetrabromocyclopropene: studies on the rearrangement of the primary Diels-Alder adduct with 2,5-dimethylfuran

The reaction of tetrabromocyclopropene and furan leads directly to 8-oxabicyclo[3.2.1]octadiene derivatives. It has been proposed that this involves an initial Diels-Alder reaction followed by rearrangement of the primary adduct. We have, for the first time, isolated a primary adduct and established through X-ray crystallographic analysis that the adduct is the product of an exo-selective addition. Kinetic studies suggest the intermediacy of charged intermediates during the rearrangement.