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Stereoselective reactions of 16-Methylene 19-Norsteroids
The influence of the 17-substituent upon epoxidation of 3-methoxy-16-methylene-estra- 1,3,5(10)-trien-17-one and the derived 17β-hydroxy and 17β-acetoxy compounds was investigated. Alkaline hydrogen peroxide epoxidation of 3-methoxy-16-methyleneestra- 1,3,5(10)-trien-17-one occurred in good yields,...
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| Format: | Thesis |
| Language: | English |
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Department of Chemistry
2016
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| Summary: | The influence of the 17-substituent upon epoxidation of 3-methoxy-16-methylene-estra- 1,3,5(10)-trien-17-one and the derived 17β-hydroxy and 17β-acetoxy compounds was investigated. Alkaline hydrogen peroxide epoxidation of 3-methoxy-16-methyleneestra- 1,3,5(10)-trien-17-one occurred in good yields, but poor stereoselectivity was obtained due to mechanistic considerations. Poor stereoselectivity was also obtained for the peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-ol, due to the pseudo-equatorial position of the 17β-hydroxyl group. However, excellent stereoselectivity was obtained using Sharpless conditions (vanadium catalyst), which gave only the epoxide syn to the hydroxyl group, in good yields. Surprisingly, peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-yl acetate favoured equatorial attack resulting in a 2:1 ratio of the (16R)- and (16S)-epoxide isomers, instead of the expected axial approach by the peracid. |
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