Facile regioselective macrocyclization of methyl cholate (1) using dimethyl α,α,α’,α’-tetramethyl-m-xylylenedicarbamate (2) by transesterification was achieved, in refluxing toluene (0.004 M), using 3% of SnCl2 and 1% of glycoluril as an additive. After a reaction time of 2 hours, the kinetically favorable 3 was obtained selectively in excellent yield (94%). Conversion of the 16-membered 3 to the 18-membered cyclophane 4 was achieved by establishing an equilibrium (7 days), to give the thermodynamically stable 4 in practical yield (68%). This mild conversion of the regiochemistry of the steroidal macrocycles is remarkable as a characteristic of the carbamoyloxa-bridged cyclophanes. The new steroidal carbamoyloxa-bridged cyclophanes is the first example of a pair of the regioisomeric steroidal cyclophanes.
通过转酯化反应,使用二甲基α,α,α’,α’-四甲基-m-二
甲苯二
羧酸酯(2)对甲基
胆酸(1)进行容易的区选择性大环化,反应在回流的
甲苯(0.004 M)中进行,添加了3%的SnCl2和1%的甘
氨酸尿
嘧啶。在反应2小时后,选择性地获得了动力学上有利的产物3,产率极高(94%)。通过建立平衡(7天),将16元环的3转化为18元环的环烯烃4,从而获得了在实际产率(68%)下热力学稳定的4。这种温和的类
固醇大环
化学区位选择性转换是
氨基醇桥连环烯烃的一大特点。新的类
固醇氨基醇桥连环烯烃是区异构体类
固醇环烯烃的一对中的第一个例子。