Asymmetric syntheses of (8R,8aS)- and (8R,8aR)-8-hydroxy-5-indolizidinones: Two promising oxygenated indolizidine building blocks
作者:HongKui Zhang、Xin Li、Huang Huang、PeiQiang Huang
DOI:10.1007/s11426-011-4256-4
日期:2011.5
Starting from the oxygenated piperidine building block 20, two synthetic approaches to new building blocks (8R,8aS)- and (8R,8aR)-8-hydroxy-5-indolizidinones 19a/19b and 15a/15b have been developed, respectively. The first one is based on the trans-diastereoselective reductive alkylation (dr = 93:7), followed by a four-step procedure; and the second one called for the RCM reaction on the N,O-acetal derived from a vinylation, which was followed by a pyrrole formation, and a stereocontrolled cis-selective (dr = 91:9) catalytic hydrogenation. Reduction of the diastereomer 15a produced (8R,8aR)-8-indolizidinol (18).
从含氧哌啶结构单元20开始,分别开发了两种合成新结构单元(8R,8aS)-和(8R,8aR)-8-羟基-5-吲哚嗪酮19a/19b和15a/15b的方法。第一种方法基于反式-非对映选择性还原烷基化(dr = 93:7),然后进行四步反应;第二种方法要求在乙烯化反应产生的N,O-乙缩醛上进行RCM反应,然后形成吡咯,最后进行立体选择性顺式(dr = 91:9)催化氢化。非对映异构体15a的还原反应生成(8R,8aR)-8-吲哚嗪醇(18)。