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

Abstract

In this study, we carried out preparative and mechanistic studies on the photochemical reaction of a series of 3-acylestrone derivatives in confined and sustainable micellar environment under steady-state conditions and the results were compared with those obtained in cyclohexane solution. The aim of this work is mainly focused to show whether the nature of the surfactant (cationic, neutral and anionic) leads to noticeable selectivity in the photoproduct formation. The 3-acylestrone derivatives underwent the photo-Fries rearrangement, with concomitant homolytic fragmentation of the ester group and [1;3]-acyl migration. This pathway afforded the ortho-acyl estrone derivatives, the main photoproducts together with estrone. However, epimerization of the ortho regioisomer 2-acetylestrone and estrone through Norrish Type I photoreaction occurred involving the fragmentation of the C-α at the carbonyl group (C-17) of the steroid. UV-visible and 2D-NMR (NOESY) spectroscopies have been employed to measure the binding constant K b and the location of the steroids within the hydrophobic core of the micelle.

Product selectivity in the photoreaction of aryl sulfonates and mesylate of estrone derivatives in sustainable and micellar media: a steady-state investigation

“…This interesting behavior has been observed early for 3-acyl and 3-arylsulfonylestrone derivatives. 16…”

“…S6 in ESI†), and these values are typical steroid values, suggesting the significant binding of sulfonic esters 1–5 with the surfactants (see Table 1). 16 Then, 1 H-NMR spectroscopy was also used as a complementary spectroscopic method in order to demonstrate the solubilization behavior of the sulfonic esters within the micelles. Thus, the differential chemical shift (Δ δ ) values were easily calculated by measuring the upfield/downfield perturbations of the surfactants’ proton chemical shifts due to the presence of the sulfonic esters (see Table 2, Fig.…”

“…Although ortho -regioisomers 1c and 2c were formed in the micellar media involving the photoepimerization reaction of compounds 1a and 2a in very low yields (>9%), a significant photostability of the ortho -regioisomers upon irradiation was observed (see Table 3). This photostability was ascribed to the sequence involving (i) an ESIPT process 16,29 between the thionyl group (SO) of the sulfone group attached to the aromatic ring A and the proton of the hydroxy group of such regioisomers, (ii) a cis – trans keto tautomerism, and (iii) heat release to the media, as can be seen in Scheme 6(a). During this sequence of events, the sole deactivation pathway is the radiationless processes; therefore, no photoepimerization of the ortho -regioisomers was observed.…”