Competing pathway involved in allylic acetoxylation of androst-5-en-17-one, and oxidation of allylic alcohols with chromium oxides.
Allylic acetoxylation of androst-5-en-17-one (1) with bromine and silver acetate gave 6 alpha- and 6 beta-acetoxyandrost-4-en-17-ones [4 (3%) and 5 (12%)] and 5 alpha-bromo-6 beta-acetoxy steroid 8 (4%) along with the expected product 4 beta-acetoxy derivative 2 (45%). Treatment of 5 alpha,6 beta-bromide 12, an intermediate of the acetoxylation reaction, with silver acetate also produced the acetates 2, 4, 5, and 8 in relative yields similar to those above. These results indicate that the 6-acetates 4 and 5 are produced through a competing pathway involving formation of a bridged carbonium ion 13 followed by attack of an acetate anion. Oxidation of the axial allylic alcohol, 5-en-4 beta-ol 3, with Jones reagent yielded no trace of the previously reported androst-5-ene-4,17-dione (18) but instead gave a 1:4 mixture of 5 beta,6 beta-epoxy-4-one 16 and 4 beta,5 beta-epoxy-6-one 17 in high yield. In contrast, a 1:4 mixture of androst-4-ene-6,17-dione (10) and compound 18 was obtained upon treatment with chromium trioxide in pyridine. Similar results were also found with the oxidation of another axial allylic alcohol, 4-en-6 beta-ol 7.
Tohoku College of Pharmacy, Sendai, Japan.
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Numazawa
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Tachibana
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Kamiza
D000107:Acetylation; D000438:Alcohols / Q000737:chemistry*; D000498:Allyl Compounds / Q000737:chemistry*; D001667:Binding, Competitive; D017608:Chromium Compounds; D003687:Dehydroepiandrosterone / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction
D000438:Alcohols; D000498:Allyl Compounds; D017608:Chromium Compounds; D003687:Dehydroepiandrosterone; C097404:androst-5-en-17-one; C023600:chromic oxide