A symmetry-allowed pericyclic reaction involving two ‘forbidden’ processes. The thermal rearrangement of (E)-2-benzylidene-(Z)-mesityl(phenyl)-methyleneindane into (Z)-2-benzyl-1-mesityl(phenyl)methyleneindene

Abstract

Electrocyclic disrotatory ring closure of (E)-2-benzylidene-(Z)-1-mesityl(phenyl)methyleneindane occurs at 180° to give (Z)-9a, 10-dihydro-5,10-diphenyl-6,8,9a-trimethyl-11H-benzo[b]fluorene, which, at this temperature, undergoes conrotatory ring opening and a concomitant suprafacial[1,7]sigmatropic change of hydrogen to yield (Z)-2-benzyl-1-mesityl(phenyl)methyleneindene.