Wavelength-Dependent Photochemistry of 4-Methoxybicyclo[3.1.0]hexenones.
Wavelength-dependent photochemistry of a series of 4-methoxybicyclo[3.1.0]hexenones is mechanistically investigated. Upon excitation of the symmetry-forbidden S(1) n-->pi state, photoisomerization is exclusively observed. By comparison of the direct and sensitized quantum yields for this particular process, the T(1) pi-->pi state, which is populated via efficient intersystem crossing as shown by phosphorescence experiments, is proven to be the reactive state. A pathway via external cyclopropane bond cleavage followed by racemization of the formed triplet biradicals reasonably accounts for the observed photostationarity. Excitation of the electric dipole allowed S(2) pi-->pi state initiates phenol formation. The T(2) n-->pi state, which could not be sensitized, gives a type-B oxyallyl zwitterion via internal cleavage as could be shown by intermolecular as well as intramolecular trapping experiments. The observed data are in good agreement with computational studies.
Dauben
William G.
WG
Department of Chemistry, University of California, Berkeley, California 94720.
Hecht
Stefan
S