Photochemistry of cyclic α-hydroxy ketones. I. The nature and genesis of the photoproducts from steroidal 5-hydroxy 6-keto steroids and related compounds

Abstract

14 (1988). Photolyses of 5-hydroxy-5a-and 5P-cholestan-6-one and their 3P-acetoxy-and 30-benzyloxy derivatives in benzene or ethanol proceed stereospecifically with retention of configuration at C-5 to give the corresponding lactones, 6-oxa-Bhomocholestan-7-ones. Photolyses of 3P-acetoxy-7a-deutero-5-hydroxy-5a-and 50-cholestan-6-ones also proceed stereospecifically to give the corresponding 5-deutero lactones. 3~-Acetoxy-5-deuteroxy-5a-and SP-cholestan-6-one give on irradiation 1:3 and 7 : l mixtures, respectively, of the corresponding 7 a a -and 7aP-deutero lactones. Irradiation of 3~-acetoxy-5-methoxy-5a-cholestan-6-one in ethanol leads to the stereoselective formation of ethyl 3P-acetoxy-5-methoxy-5,6-seco-5a-cholestan-6-oate, while that of 3P-acetoxy-Sa-cholestan-6-one gives mainly photoreduction products. These observations are interpreted in terms of a-cleavage of the C-5-C-6 bond of the ketols to give alkyl acyl diradicals that undergo hydrogen transfer to give hydroxy ketenes, which then form the lactones. It is proposed that retention of configuration at C-5 results from two major factors-the nonplanar geometry of the hydroxyalkyl radical center, and fast hydrogen transfer in the diradical, the latter resulting from restricted rotation about the C-9-C-10 bond. The specific transfer of the 7a-deuterium atom in the 7a-deutero ketols is attributed to these factors and to the preferred direction of opening to the diradical on a-cleavage. The 0-deuterium labelling results are interpreted in terms of product development control in the conversion of the hydroxy ketenes to the lactones and are in accord with restricted rotation about the C-9-C-I0 bond. The photolysis of 3P-acetoxy-5-amino-5a-cholestan-6-one proceeds stereoselectively to give the SP-lactam analogue of the SP-lactone formed from the analogous Sa-ketol.SHIRLEY STIVER et PETER YATES. Can. J. Chem. 66, 214 (1988). La photolyse des hydroxy-5 5 a -et SP-cholestanones-6 et de leurs dCrivCs acCtoxy-3P et benzyloxy-3P, dans le benzkne ou I'tthanol, se produit d'une faqon stCrCospCcifique, avec rCtention de configuration en C-5, pour conduire aux lactones correspondantes, oxa-6 B-homocholestanones-7. La photolyse des acCtoxy-3P deutCro-7a hydroxy-5 5 a -et SP-cholestanones-6 se produit aussi d'une faqon stCrCospCcifique pour conduire aux lactones correspondantes deutkro-5. Par irradiation, les acCtoxy-3P deutCroxy-5 5 a -et 5P-cholestanones-6 conduisent respectivement a des melanges 1:3 et 7:l des lactones correspondantes deutCro-7aa et -7aP. L'irradiation de I'acCtoxy-3P mCthoxy-5 5a-cholestanone-6, dans I'Cthanol, conduit la formation stCrCosClective de I'acCtoxy-30 mCthoxy-5 sCco-5,6 5a-cholestanoate-6 d'Cthyle alors que celles de I'acetoxy-3P 5a-cholestanone-6 donne principalement des produits de photorCduction. On interprkte ces rCsultats en fonction d'un clivage-a de la liaison C-5/C-6 des cCtols qui fournit des diradicaux alkyle acyle qui subissent des transferts d'hydrogene conduisant des hydroxy-cCtenes qui forment alors des lactones. On suggkr...

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

“…The photochemical behavior of steroids in solution was completely studied in terms of photorearrangement, photoaddition, photoreduction and photooxidation reactions throughout the years (9), and photochemical approaches toward the synthesis of natural products have been applied with success (10). The photochemistry of steroids have been studied in terms of preparative, mechanistic and taking into account the stereospecificity of the photoreaction and some interesting examples are depicted in Scheme 1 (11)(12)(13)(14)(15)(16)(17)(18)(19). Indeed, photoinduced lactonization reaction of some cholestan-6-one derivatives provided efficiently 6-oxa-B-homocholestan-7-ones with retention of the configuration at C-5 (12).…”

“…The photochemistry of steroids have been studied in terms of preparative, mechanistic and taking into account the stereospecificity of the photoreaction and some interesting examples are depicted in Scheme 1 (11)(12)(13)(14)(15)(16)(17)(18)(19). Indeed, photoinduced lactonization reaction of some cholestan-6-one derivatives provided efficiently 6-oxa-B-homocholestan-7-ones with retention of the configuration at C-5 (12). Likewise, direct irradiation of 3a-(dimethylphenylsilyloxy)-5a-androstane-6,17-dione and its 3b isomer gave two distinct photoproducts arising from the photoreduction and the Norrish Type-I reactions of the steroids.…”

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

“…Along the past years, some interesting examples of the photochemistry of steroids have been studied in terms of preparative, mechanistic and analyzing the stereospecificity of the photoreaction [16][17][18][19][20][21]. Indeed, photoinduced lactonization reaction of some cholestan-6-one derivatives provided efficiently 6-oxa-B-homocholestan-7-ones with retention of the configuration at C-5 [16].…”

“…Along the past years, some interesting examples of the photochemistry of steroids have been studied in terms of preparative, mechanistic and analyzing the stereospecificity of the photoreaction [16][17][18][19][20][21]. Indeed, photoinduced lactonization reaction of some cholestan-6-one derivatives provided efficiently 6-oxa-B-homocholestan-7-ones with retention of the configuration at C-5 [16]. Likewise, direct irradiation of 3α-(dimethylphenylsilyloxy)-5α-androstane-6,17-dione and its 3β isomer gave two distinct photoproducts arising from the photoreduction and the Norrish type I reactions of the steroids.…”