A Novel Photochemical Vinylcyclopropane Rearrangement Yielding 6,7-Dihydro-5<i>H</i>-benzocycloheptene Derivatives

Abstract

[reaction: see text] 1-Substituted 1-(2,2-diphenylvinyl)cyclopropanes with electron-accepting groups at C1 undergo a novel rearrangement to benzocycloheptenes on triplet-sensitized irradiation. In some instances competition between rearrangement to cyclopentenes and formation of cycloheptenes takes place. When electron-acceptor groups are not present at C1, conventional ring opening to cyclopentenes occurs exclusively. A mechanism involving intramolecular SET from the diphenylvinyl unit to the electron-acceptor group is proposed for this novel photoreaction.