Organic photochemistry. 95. Antenna-initiated photochemistry of distal groups in polyfunctional steroids. Intramolecular singlet and triplet energy transfer in 3.alpha.-(dimethylphenylsiloxy)-5.alpha.-androstan-17-one and 3.alpha.-(dimethylphenylsiloxy)-5.alpha.-androstane-11,17-dione

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

“…Therefore, after accurate rationalization of the results, we can conclude that (1) the excited triplet state of estrone phenyl sulfonate 1 is not the photoreactive state in the photo-Fries rearrangement reaction and (2) the conversion of estrone 5 into lumiestrone 6 certainly involves the triplet excited state because the photoepimerization reaction was efficiently quenched by TMDO. The photoepimerization reaction of estrone 5 is in agreement with similar results reported in the literature such as the involvement of a triplet state in the photoepimerization reaction of cyclic ketones (16,42,45). Likewise, we have previously demonstrated that direct irradiation of estrone methyl ether furnished lumiestrone methyl ether involving the photoepimerization of methyl group at C-13 through a Norrish Type-I mechanism (39).…”

“…On the other hand, epimerization of compounds 1a, 2a and 3a to photoproducts 1c, 2c and 3c, respectively, is due to the non-planarity of the arylsulfonyl group with the benzene moiety disfavoring the intramolecular hydrogen bonding between the thionyl group and the hydroxyl group. Therefore, in these cases, the ESIPT process is not a competitive pathway and the epimerization reaction of the carbonyl group proceeds smoothly because an intramolecular triplet photosensitization process occurs from the aryl moiety to the carbonyl group at C-17 of compounds 1c, 2c and 3c accordingly which was previously reported in the literature for 3a-dimethylphenylsilyloxy androstanone derivatives (16,42) and 3-acylestrone derivatives (39).…”

“…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. An antenna-photosensitization process from the arylsilyloxy group to the carbonyl groups through triplet and singlet energy transfers accounts for this particular behavior (16).…”

“…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).…”

Isolation and Characterization of Photodegradation Impurity in Budesonide Drug Product Using LC-MS and NMR Spectroscopy

“…Moreover, the Morrison established through a series of elegant papers [6] [7] [8] [9] that intramolecular energy transfer (both singlet-singlet and triplet-triplet) occurred from the phenyl "antenna" to C17 keto group by the way of throughbond mechanism. This has led to a different photochemistry observed by the direct excitation of ketone chromophore.…”