Selectivity in the Photo-Fries Rearrangement of Some Aryl Benzoates in Green and Sustainable Media. Preparative and Mechanistic Studies

Abstract

Irradiation of a series of p-substituted aryl benzoates under N2 atmosphere in homogeneous and micellar media was investigated by means of steady-state condition and of time-resolved spectroscopy. A notable selectivity in favor of the 2-hydroxybenzophenone derivatives was observed in micellar media. The benzophenone derivatives were the main photoproduct. On the other hand, in homogeneous media (cyclohexane, acetonitrile, and methanol) the observed product distribution was entirely different, viz. substituted 2-hydroxybenzophenones, p-substituted phenols, benzyl and benzoic acid were found. The binding constants in the surfactant were also measured and NOESY experiments showed that the aryl benzoates were located in the hydrophobic core of the micelle. Laser flash photolysis experiments led to the characterization of both p-substituted phenoxy radical and substituted 2-benzoylcyclohexadienone transients in homogeneous and micellar environment.

Photochemical Behavior of Some Estrone Aryl and Methyl Sulfonates in Solution: Preparative and Mechanistic Studies

“…In addition, we have also contributed to show how important is the application of the photo-Fries rearrangement reaction in the preparation of 2,2-dimethyl-4-chromanone derivatives (33,34) and carbazole derivatives (35,36). Recently, we were able to show the selectivity and the effect of surfactant micelles on the photo-Fries reaction of an assortment of substituted acetamides (37) as well as substituted aryl benzoates (38) and also, the photochemical behavior of 3-aryloxy estrone derivatives in solution (39). Therefore, we present herein our work on the direct irradiation of estrone derivatives 1-4 (see Chart 1) in term of product distribution, triplet photosensitization and chemical quenching of the photochemical reaction.…”

Induced selectivity in the photochemistry of estrone derivatives in sustainable and micellar environment: preparative and mechanistic studies

“…Therefore, the confined environment provided by the hydrophobic core of the micelle can be considered as a micro reactor where (photo)reactions can take place, the reactivity of radical species generated can be controlled and, at the same time, can be helpful to direct the selectivity of the (photo)products. Some interesting examples of photoreaction carried out in micellar media as optimal micro reactor that can control the selectivity and yield of the photoproducts can be found in the literature [42][43][44][45] and our research group has also contributed with several examples [46][47][48][49].…”

“…In this regard, UV-visible spectroscopy studies of 3-acylestrone derivatives (1-3) in micellar solution were conducted in order to determine the binding constant (K b ) between the surfactants (SDS, CTAC and Brij-P35) and the steroids 1-3. The methodology employed in this study has been previously reported for the determination of binding constants of aryl acetamide and aryl benzoates [46,47]. The analysis of bathochromic and hyperchromic shifts of the lower energy absorption band of the steroids 1-3 in water by addition of increasing amounts of surfactant led to evaluate the extent of binding of steroids to the surfactants within the hydrophobic core of the micelle (batho-and hyperchromic shifts, see Figures S5-S7 in Supporting Information).…”

“…Taking into account that a differential chemical shifts (Δδ) was observed in the presence of esters 1-3, the next step was to confirm qualitatively the location of the esters within the hydrophobic core of the micelle employing 2D NMR spectroscopy. The extent of co-aggregation in water between two different kinds of surfactants or the localization of guest molecules within the micelle have been often determined using NOESY experiments [46][47][48][49][73][74][75][76][77]. In addition, these experiments give satisfactory results when cross-peaks between diagnostic signals of the substrates and the surfactants, respectively, are noticed in the corresponding contour plots [46][47][48][49].…”

“…The extent of co-aggregation in water between two different kinds of surfactants or the localization of guest molecules within the micelle have been often determined using NOESY experiments [46][47][48][49][73][74][75][76][77]. In addition, these experiments give satisfactory results when cross-peaks between diagnostic signals of the substrates and the surfactants, respectively, are noticed in the corresponding contour plots [46][47][48][49].…”