Remarkable Differences in Photo and Thermal (Acid-catalyzed) Reactivities between orthoand para-Acylcyclohexadienones as Essential Factors Determining the Overall Efficiency of the Photo-Fries Rearrangement

Successful isolation of "ortho" and "para"-acylcyclohexadienones allowed us to comparatively study their ground- and excited-state behavior under a variety of conditions. In neutral solutions, the two isomeric cyclohexdienones showed completely different reactivities for photochemical and thermal reactions, while in acidic methanol both quantitatively afforded the corresponding transesterification product and naphthol. These studies help us understand the detailed photo-Fries rearrangement mechanism, which involves several crucial photochemical and thermal steps.