Numazawa M, Tachibana M, Kamiza M
Tohoku College of Pharmacy, Sendai, Japan.
Steroids. 1995 Aug;60(8):499-505. doi: 10.1016/0039-128x(95)00057-w.
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.
用溴和醋酸银对雄甾-5-烯-17-酮（1）进行烯丙基乙酰氧基化反应，得到了6α-和6β-乙酰氧基雄甾-4-烯-17-酮[4（3%）和5（12%）]以及5α-溴-6β-乙酰氧基甾体8（4%），同时还生成了预期产物4β-乙酰氧基衍生物2（45%）。将乙酰氧基化反应的中间体5α,6β-溴化物12用醋酸银处理，也生成了醋酸酯2、4、5和8，其相对产率与上述情况相似。这些结果表明，6-醋酸酯4和5是通过一条竞争途径生成的，该途径涉及形成一个桥连碳正离子13，随后醋酸根阴离子进行进攻。用琼斯试剂氧化轴向烯丙醇5-烯-4β-醇3，未检测到先前报道的雄甾-5-烯-4,17-二酮（18）的痕迹，而是高产率地得到了5β,6β-环氧-4-酮16和4β,5β-环氧-6-酮17的1:4混合物。相比之下，用吡啶中的三氧化铬处理得到了雄甾-4-烯-6,17-二酮（10）和化合物18的1:4混合物。对另一种轴向烯丙醇4-烯-6β-醇7进行氧化时也发现了类似的结果。
