Photo-Fries Rearrangement of Some 3‑Acylestrones in Homogeneous Media: Preparative and Mechanistic Studies

MATÍAS I. QUINDT; SERGIO M. BONES; GABRIEL F. GOLA; JAVIER A. RAMIREZ

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 anitrogen atmosphere in cyclohexane, acetonitrile (MeCN), andmethanol (MeOH) was investigated under steady-state conditions.The molecules underwent the photo-Fries rearrangement, withconcomitant homolytic fragmentation of the ester group and [1;3]-acyl migration. This pathway afforded the ortho-acyl estronederivatives, the main photoproducts, together with estrone. Duringthe irradiation of 3-benzoyl estrone, epimerization of estronethrough the Norrish type I reaction occurred, providing lumiestroneas the photoproduct. This photoreaction involves the fragmentationof the C-α at the carbonyl group (C-17) of the steroid. On the otherhand, epimerization of ortho-regioisomer 2-acetyl estrone occurredduring the irradiation of 3-acetyl estrone. Photosensitization withacetone and chemical quenching with N,N,N,N-tetramethyldiazetinedioxide of the photo-Fries reaction confirmed that thephotoreaction took place from the singlet excited state while the Norrish type I reaction proceeds efficiently from the tripletexcited state. Solvent effects, as well as the nature of the acyl group on the photoreactions, were also studied