Synthesis and Dimerization of Bicyclo [4.4.1] undec-1 (11)-ene,a Bridged trans-Cycloheptene

The synthesis of bicyclo 4.4.1] undec-1 (11)-ene ( 5 ) by intramolecular Wittig reaction is described. The Bredt olefin could not be isolated, but dimerized rapidly to a novel compound 15 containing a cyclopropane ring. The olefin 5 was trapped in situ by 2,5-diphenylbenzo c]furan.