Enantioselective syntheses of both (20R)- and (20S)-de-AB-cholesta-8(14), 22-dien-9-one (22 and 23), which are potential intermediates leading to vitamin D3, steroids and their analogues, have been developed. The (3R)-methyl-cyclopentanone 12 was obtained through a known procedure starting with (S)-2, 3-O-isopropylideneglyceraldehyde (8) or through inversion of the C6 position in compound 5 using the Mitsunobu reaction followed by orthoester Claisen rearrangement. The construction of the trans-angularly methylated CD ring was accomplished through stereo- and regioselective Michael addition of the lithium enolate of 12 to α-silylated vinyl ketone, followed by intramolecular aldol condensation.
(20R)- 和 (20S)-de-AB-cholesta-8(14)、22-dien-9-one(22 和 23)的对映选择性合成,它们是产生
维生素 D3、类
固醇及其类似物的潜在
中间体,已经开发出来。 (3R)-
甲基-
环戊酮 12 通过已知的程序获得,从 (S)-2, 3-O-异丙叉基
甘油醛 (8) 开始,或通过使用 Mitsunobu 反应然后进行原酸
酯 Claisen 重排来反转化合物 5 中的 C6 位。跨角
甲基化
CD环的构建是通过12的
烯醇
锂与α-甲
硅烷基化
乙烯基酮的立体和区域选择性迈克尔加成,然后进行分子内羟醛缩合来完成的。