3,4-Homoadamantadiene:  Generation and Regioselective [2+2] Cycloaddition of a Novel Tricyclic Bridgehead Allene

Dehalogenation of 3-bromo-4-iodo-4-homoadamantene with n-BuLi gave rise to 3,4-homoadamantadiene, a novel tricyclic bridgehead allene, which readily dimerized to head-to-head and head-to-tail [2+2] cycloadducts in a ratio of 96:4. Trapping with 1,3-diphenylisobenzofuran was successful to yield the corresponding Diels−Alder adduct.