GENERATION AND OLIGOMERIZATION OF BICYCLO[2.2.2]OCTYNE AND PROPERTIES OF TRIS(BICYCLO[2.2.2]OCTENO)BENZENE OBTAINED FROM THE LINEAR TRIMER

Reaction of 2,3-dibromobicyclo[2.2.2]oct-2-ene (10) with n-butyllithium in THF at -78-degrees-C affords a series of oligomeric dibromides 11 (n = 2-5), which are composed of linearly bonded bicyclo[2.2.2]oct-2-ene units. A trapping experiment indicated that the reaction proceeds via formation of a highly strained acetylene, bicyclo[2.2.2]octyne (18), as a reactive intermediate. Upon treatment with sodium naphthalenide, the trimer 11 (n = 3) reductively cyclizes to tris(bicyclo[2.2.2]octeno)benzene (12) in high yield. The benzene 12 exhibits a reversible oxidation wave at +1.25 V vs Ag/AgNO3 on cyclic voltammetry and gives a stable cation radical 12.+ electrolytically or by oxidation with H2SO4 in air. In FSO3H, 12 is 100% protonated to give the arenium ion 22. The results of variable-temperature C-13 NMR study indicate that the activation energy for the intermolecular proton transfer of 22 is lower than that for the hexamethylbenzenium ion (23). The rate of intramolecular hydrogen migration is also much faster in 22. These results are in agreement with the relative instability of 22 (pK(AH+) -10.2) as compared with 23 (pK(AH+) -9.01).