A Flexible Route to [4.1.1]Propellanes

Reaction of Diels–Alder adducts of 1-bromo-2-bromomethylcyclopropene and either 1,3-dienes or furans with n- or t-butyllithium leads to a 1,3-dehalogenation to produce [4.1.1]propellanes. The oxygen bridged propellane derived from furan reacts with a second mole equivalent of n-butyllithium by cleavage of the bridge with allylic rearrangement and the formation of a cis-2-butyl[4.1.1]propell-3-en-1-ol. Iodination of this leads to rearrangement with the production of 6-methylene-8-oxabicyclo[3.2.1]oct-2-enes. The corresponding adducts of 1-bromo-2-bromoethylcyclopropene do not undergo 1,4-debromination under the conditions examined.