Synthetic Studies toward Galbulimima Alkaloid (−)-GB 13 and (+)-GB 16 and (−)-Himgaline
作者:Weiwei Zi、Shouyun Yu、Dawei Ma
DOI:10.1002/asia.201000556
日期:2011.2.1
cleavage of the ketal protecting group. SmI2‐mediated carbonyl–alkene reductive coupling of 46 proceeded smoothly in refluxing tetrahydrofuran to deliver pentacyclic intermediate 49, which was oxidized with 2‐iodoxybenzoic acid and then treated with trifluoroacetic acid to furnish (−)‐GB 13. The overall yield was 6.1 % over 19 linear steps. By following the known procedure, our synthetic (−)‐GB 13 was converted
将(S)-3-氨基丁烷-1-醇与1,3-环己烷二酮缩合,然后进行分子内烷基化,得到双环烯胺32,其通过非对映选择性氢化转化为烯酮35。Mukaiyama–Michael向35中添加了双环甲硅烷基烯醇醚,随后通过氧化/还原策略进行了立体化学转化,从而获得了内酯41。用LAH还原内酯41后,通过自发的分子内羟醛反应和缩酮保护基的裂解,进行Swern氧化,得到烯酮46。SmI 2介导的羰基-烯烃还原偶合反应为46在四氢呋喃中回流可顺利进行,得到五环中间体49,该中间体用2-碘氧苯甲酸氧化,然后用三氟乙酸处理,得到(-)-GB13。在19个线性步骤中,总收率为6.1%。按照已知的程序,我们的合成(-)-GB 13被转化为hegaline。此外,从内酯41开始,实现了(+)-GB 16的首次全合成,这是一种新分离的gabulimima生物碱家族成员。该合成的特征是胺和1,3-二酮部分之间的分子内缩合。