The reaction sequence 9→11→ 20→23 was carried out as model investigation for the total synthesis of 20-methyl-pregn-4-en-3-on (23) via 9 obtainable by cyclization of tetraen-ol 1. A-nor-steroid-3(5),8(14) diene 9 together with isomers 10–12 was prepared by HBr induced rearrangement of the cyclosteroids 6/7, obtained from ergosterin. 10 and 12 were isomerized on palladium charcoal to 9 or 11 respectively;
进行反应顺序9 → 11 → 20 → 23作为模型研究,通过四烯醇1的环化反应可得到9,从而合成20-甲基-pregn-4-en-3-on(23)。A-nor-steroid-3(5),8(14)二烯9及其异构体10-12是通过HBr诱导从
麦角固醇获得的环类
固醇6/7的重排而制备的。10和12在
钯炭上分别异构化为9或11;HBr可以将9异构化为11。11的区域选择性氢化产生单烯20,其被转化为23。