The photo-Fries rearrangement of some 3-acylestrone in homogeneous media. Preparative and mechanistic studies.

QUINDT, MATIAS; GOLA, GABRIEL F.; RAMIREZ, JAVIER; BONESI S. M.

JOURNAL OF ORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2019 vol. 84 p. 7051 - 7065

0022-3263

Irradiation of a series of 3-acylestrones under nitrogen atmosphere in cyclohexane, MeCN and MeOH was investigated under steady-state conditions. The molecules 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. During the irradiation of 3-benzoyl estrone, epimerization of estrone through the Norrish Type I reaction occurred, providing lumiestrone as the photoproduct. This photoreaction involves the fragmentation of the C-at the carbonyl group (C-17) of the steroid. On the other hand, epimerization of ortho-regioisomer 2-acetyl estrone occurred during the irradiation of 3-acetyl estrone. Photosensitization with acetone and chemical quenching with N,N,N,N-tetramethyldiazetinedioxide of the photo-Fries reaction confirmed that the photoreaction took place from the singlet excited state while the Norrish Type I reaction proceeds efficiently from the triplet excited state. Solvent effects, as well as the nature of the acyl group on the photoreactions, were also studied.