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Hirundigenin can easily be converted into anhydrohirundigenin by thermal dehydration. Both substances are stable to alkali but unstable under acid conditions. Dehydrogenation of anhydrohirundigenin, using selenium at 310°, gave a mixture of 2-methylphenanthrene (29), 1, 2-dimethyl-phenanthro [1,2-b] furan (30) and 1-ethyl-2-methyl-phenanthro [1,2-b] furan (32), all of which could be isolated in crystalline form. The last two substances are new and their structures were confirmed by synthesis. Through these results, as well as by further reactions and spectra, it could be shown that hirundigenin and anhydrohirundigenin are 16-methyl-15-oxapregnane derivatives, further, that they have two epoxide rings and that they probably have the structures 7 and 11. These structures were proved by O. Kennardet. al. through X-ray studies of p-bromobenzoyl-anhydrohirundigenin (13). As far as we know, 15-oxasteroids had not yet been found in nature. |
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