A three-state model for the photo-Fries rearrangement

Abstract

A three-state model for the photo-Fries rearrangement (PFR) is proposed based on multiconfigurational calculations. It provides a comprehensive mechanistic picture of all steps of the reaction, from the photoabsorption to the final tautomerization. The three states participating in the PFR are an aromatic ππ*, which absorbs the radiation; a pre-dissociativenπ*, which transfers the energy to the dissociative region; and a πσ*, along which dissociation occurs. The transfer fromππ* to nπ* involves pyramidalization of the carbonyl carbon, while transfer fromnπ* to πσ* takes place through CO stretching. Different products are available after a conical intersection with the ground state. Among them is a recombined radical intermediate, which can yield ortho-PFR products after an intramolecular 1,3-H tunneling. The three-state model is developed for phenyl acetate, the basic prototype for the PFR, and it reconciles the theory with a series of observations from time-resolved spectroscopy. It also delivers a rational way to optimize PFR yields, since, as shown for four different systems, diverse substituents can change the energetic order of theππ* and nπ* states, preventing or enhancing the PFR.

Theoretical Analysis of Properties of Ground and Excited States for Photodissociation of the C–O Bond in Polycarbonates

“…When the C29–O32 distance is shortened to 1.379 Å and O32–C33 distance is elongated to 1.382 Å, a pyramidalized structure (see Figure S5) appears. This structure can be considered as the pre-dissociative structure, which was described by Toldo et al . Then, the decrease in C29–O32 distance and increase in O32–C33 distance occur suddenly.…”

“…Grimme in 1992 reported photo-Fries-type cleavage of phenyl acetate PhOC­(O)­CH 3 using semi-empirical methods, and the results show that a barrier of 0.9–1.2 eV is necessary to complete the photodissociation of phenyl acetate and the 1 πσ* state (a singlet state via the π (O of Ph–O) → σ (OC–O) * transition) is the dissociative state. However, this significant barrier caused due to geometric constraints only gave a limited explanation under the semi-empirical level 30 years ago and does not align with picosecond timescale observations in recent experiments. , Recent insights into the mechanisms of the photo-Fries reaction were provided by Toldo et al These authors examined the detailed mechanism of photo-Fries rearrangement for phenyl acetate with multiconfigurational theoretical methods. The results indicate that the photo-induced bond cleavage is caused by the interaction of three singlet electronic states.…”

“…However, this significant barrier caused due to geometric constraints only gave a limited explanation under the semiempirical level 30 years ago and does not align with picosecond timescale observations in recent experiments. 15,16 Recent insights into the mechanisms of the photo-Fries reaction were provided by Toldo et al 17 These authors examined the detailed mechanism of photo-Fries rearrangement for phenyl acetate with multiconfigurational theoretical methods. The results indicate that the photo-induced bond cleavage is caused by the interaction of three singlet electronic states.…”

Diversity-oriented synthesis of medium-sized cyclophanes via the photo-fries rearrangement of N-aryl lactams

“…32 The radical mechanism of the photo-Fries rearrangement is well understood and it is known that this rearrangement mainly occurs via an excited singlet state. [33][34][35][36][37][38] Earlier studies on the distribution of photo-Fries rearrangement reaction products of arylamides in isotropic media yielded ortho and para rearranged photoproducts as well as the corresponding aryl amine. Despite being one of the older and more well-studied photochemical organic reactions, the photo-Fries rearrangement has seldom been used in complex settings and rarely to form large rings.…”

Phototriggered Ketone Formation from an Aminocyclopropenone and a Carboxylic Acid

“…The phototriggered rearrangement of the acyloxyenamine probably consists of homolysis/recombination processes like photo-Fries rearrangement, as shown in Scheme . Excitation of acyloxyenamine 7 would produce an enoxyl radical and an acyl radical followed by recombination of the radicals to form the ketones.…”