Photo-Fries rearrangement of aryl acetamides: regioselectivity induced by the aqueous micellar green environment

Abstract

Photochemical reactions tend to give more than one photoproduct. However, such a reaction can be a powerful synthetic tool when it is possible to conduct it in regioselective conditions yielding a single photoproduct. Water-surfactant solutions as reaction media can be considered as an approach in this context because they show products with different features than those from isotropic solutions. Here we describe results obtained from studying the effect on the prototypical photoreaction, known as the photo-Fries reaction of several substituted acetanilides and α-naphthyl acetamide within surfactant micelles (ionic and non-ionic micelles). This reaction involves homolytic cleavage of a C-N bond to yield a singlet radical pair. The surfactant micelles control the rotational and translational mobility of the radical pair, resulting in noticeable photoproduct selectivity.

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).…”

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).…”

“…This behavior can be ascribed to the high disorder of the hydrocarbon chains within the hydrophobic core of the micelles favoring the intimate interaction of the esters with all the proton nuclei of the hydrocarbon chains of the surfactant and consequently, displaying a differential chemical shifts of each proton nuclei. This methodology has been previously used to analyze the effect of substrates on the chemical shifts of the surfactants [46,73].…”

A three-state model for the photo-Fries rearrangement

“…[11][12][13] Compared to its thermal version, the Lewis-acid catalyzed Fries rearrangement, PFR has an additional benefit of being a greener synthetic route, since it can be achieved under milder conditions. 3,14,15 Given its importance for synthesis, it is not surprising that PFR has been the subject of numerous investigations in the past. Nevertheless, the conceptual theoretical knowledge of this reaction is still incipient [36][37][38] and, as we shall see, even the full set of electronic states involved in the reaction has not been yet identified.…”