olestane-6-spiro-2′-(1′,3′-dioxolane)(2) and its 5β-epimer (3) undergo cleavage of the acetal ring with skeletal rearrangement to give 5-(2-hydroxyethoxy)-3β-methoxy-4aα-methyl-A-homo-B-nor-5β-cholestan-4aβ-ol (5) upon treatment with MeMgl in refluxing toluene; in a second rearrangement the A-homo-B-norsteroid (5) is smoothly converted into 3β-methoxy-5-methyl-5α-cholestan-6-one (7).
5-羟基-3β-甲氧基-
5α-胆甾烷-6-螺环-2'-(1',3'-二
氧戊环)(2)及其5β-顶基(3)均发生
乙醛环裂解,并发生骨架重排至在回流的
甲苯中用MeMgl处理后得到5-(2-羟基乙氧基)-3β-甲氧基-4aα-甲基-A-均一-B-nor-5β-
胆甾醇-4aβ-醇(5);在第二次重排中,将A-同型B-降甾体(5)平稳地转化为3β-甲氧基-5-甲基-5α-
胆甾醇-6-一(7)。