SOLVENT EFFECTS ON THE PHOTOCHEMICAL ISOMERIZATION OF 5-CYANO-5H-BENZOCYCLOHEPTENE.

Article abstract of DOI:10.1246/bcsj.56.3449

The photochemical reaction of 5-cyano-5H-benzocycloheptene has been studied kinetically in various solvents. The main reactions were (1) a 1,7-hydrogen shift, with simultaneous cyclization, to give 7b-cyano-1a,7b-dihydro-1H-cyclopropa left bracket a right bracket naphthalene and (2) a 4 pi -electrocyclic ring closure to give cyclobutenes. The former reaction was found to show rather complicated solvent effects, but the latter was accelerated in less polar solvents. The conformational equilibrium between exo- and endo-forms was also observed in the NMR spectra under various conditions. From a consideration of the solvent effects on the product distribution, the ground-state conformations could be reflected in the ratio of the exo and endo forms of the cyclization products.