corresponding to the BC ringsystem was prepared from the 8-membered ring 6 by successive trimethylaluminium-assisted stereoselective conjugated addition and intramolecular samarium(II) iodide-mediated double aldol cyclization. The ABC-ring system 4 was constructed by stereoselective homo-allylation and pinacol coupling cyclization with low-valent titanium. The synthesis of new 19-hydroxytaxoid 36 was accomplished
具有双羟醛骨架的新型 19-羟基紫杉醇 36 的立体选择性合成是通过 B 到 BC 到 ABC 环构建的方式实现的。通过分子内碘化钐 (II) 介导的双羟醛环化反应,由环氧酮醛 8 以高收率合成了对应于 19-羟基紫杉醇 B 环的光学活性 8 元环 6。对应于BC环系的双环化合物5是由8元环6通过连续的三甲基铝辅助立体选择性共轭加成和分子内碘化钐(II)介导的双羟醛环化反应制备的。ABC环系统4是通过立体选择性同烯丙基化和频哪醇偶联环化与低价钛构建的。