Investigation of the photo-Fries rearrangement reactions of 1- and 2-naphthyl acetates

Abstract

The investigation of the photo-Fries reaction of 1- and 2-naphthyl acetates (1- and 2-NAs) was performed using stationary photolysis, laser flash photolysis and steady state and time-resolved chemically induced dynamic nuclear polarization (CIDNP). The transient absorption spectra of the 1- and 2-napthoxyl radicals and the 1-NA and 2-NA triplet states were detected, and the quantum yields and absorption coefficients were obtained. The influence of a triplet quencher on the napthoxyl radical quantum yield was studied, and the singlet nature of the primary radical pair was confirmed for both initial compounds. On laser flash photolysis of 1-NA, the formation of the ortho product was directly detected, and the rate constant of the [1,3] hydrogen shift reaction was established. The signs of the CIDNP signals during the photolysis of 2-NA point to a singlet precursor of the radical pair giving rise to the rearrangement products, and to a triplet precursor for the disproportionation products of the parent radical pair. A comparison of the slopes of the Stern-Volmer plots for the rearrangement product quantum yield, for triplet CIDNP, and for the optically detected 2-NA triplet state confirms the previously reported assumption about the main role of the excited singlet state and the involvement of two different triplet states in the reaction. A general kinetic scheme for 1- and 2-NA photolysis is proposed.