Synthesis of the cholestane derivative (V) having a bridged bicyclo [2. 2. 2] octane ring system of the atisine type was attained by various routes starting from 5α-cyanocholestan-3-one (II) as illustrated in Chart 4. The route through the ketal aldehyde (X) and 5α-vinylcholestan-3-one 3-ethylene ketal (XV), the key intermediate for the present synthesis, was found to be most advantageous. However, another route through the bridged acetoxy mesylate (XVI) is also thought to be important, since this intermediate is commonly used for the synthesis of the kaurene-type bridged ring compounds as decribed in the preceding paper. The allylic alcohol function of the atisine type was introduced at the corresponding position with opposite configuration of the hydroxy group giving compound (XXXVIII).
如图 4 所示,从 5α-
氰基胆甾烷-3-酮(II)开始,通过不同路线合成了具有桥接双环 [2.通过酮醛(X)和 5α-vinylcholestan-3-one 3-ethylene ketal(XV)(本合成的关键中间体)的路线被认为是最有利的。然而,通过桥联乙酰氧基
甲磺酸酯(XVI)的另一条途径也被认为是重要的,因为这种中间体通常用于合成前一篇论文中描述的高烯类
桥环化合物。在相应的位置上引入与羟基构型相反的阿蒂辛型烯丙基醇功能,得到化合物 (XXXVIII)。