5(10)-trien-7-one (II) which is rapidly and completely isomerised at C-8 under more vigorous conditions. Dehydration of the alcohols derived from (II) and its 8-epimer (III) with phosphorus pentoxide yields 1-methyl-19-norcholesta-1,3,5(10),8(14)-tetraene as the major product while (XVII) and its 8-epimer (XVIII) predominate with phosphoryl chloride in pyridine as the reagent.
在
甲苯酸酐中用
甲苯-对
磺酸处理cholesta-1,3,5-trien- 7-one得到7-乙酰氧基-1-甲基-19-norcholesta-1,3,5(10),6-四烯(四)高产。该烯醇
乙酸酯的轻度
水解得到1-甲基-19-降胆甾烯-1,3,5(10)-
三烯-7-一(II),其在更剧烈的条件下在C-8迅速且完全异构化。用五氧化二
磷将(II)及其8-末端(III)衍生的醇脱
水,得到以1-甲基-19-降胆甾烯-1,3,5(10),8(14)-四烯为主要产物,而( XVII)及其8-末端(XVIII)以
吡啶中的
磷酰
氯为试剂占主导地位。