Treatment of hexabromocyclopentadiene (1) with sodium methoxide in methanol-glyme provides 1, 2, 3, 4-tetrabromo-5, 5-dimethoxycyclopentadiene (6). The reactivity of this new diene in the Diels-Alder reaction has been determined with a number of dienophiles. The greater reactivity of ketal 6 towards maleic anhydride compared to cyclopentadiene suggests that 6 behaves as an electron-rich diene in the Diels-Alder reaction.
