First Steroidal Carbamoyloxa-Bridged Cyclophanes: Regioselective Macrocyclization of Methyl Cholate by Double Transesterification
作者:Shin Irie、Makoto Yamamoto、Keiki Kishikawa、Shigeo Kohmoto、Kazutoshi Yamada
DOI:10.1055/s-1996-4343
日期:1996.9
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。