Pyrrolizidines, indolizidines and quinolizidines via a double reductive cyclisation protocol: concise asymmetric syntheses of (+)-trachelanthamidine, (+)-tashiromine and (+)-epilupinine
作者:Marta Brambilla、Stephen G. Davies、Ai M. Fletcher、Paul M. Roberts、James E. Thomson、David Zimmer
DOI:10.1016/j.tet.2016.09.006
日期:2016.11
The asymmetric syntheses of pyrrolizidine, indolizidine and quinolizidine alkaloids have been achieved using the diastereoselective conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to α-alkenyl-α,β-unsaturated esters followed by diastereoselective protonation of the resultant enolates as the key stereodefining steps. The azabicyclic scaffolds were then efficiently constructed upon sequential
使用锂(R)-N-苄基-N-(α-甲基苄基)酰胺的非对映选择性共轭加成到α-烯基-α,β-不饱和酯中,然后进行非对映选择性,吡咯并立定,吲哚并立定和喹喔啉生物碱的不对称合成合成的质子化成为关键的立体定义步骤。然后,通过依次氧化所得β-氨基酯中的烯烃单元和相应的二醛进行氢解N-脱苄基反应,可以有效地构建氮杂双环支架,这与双还原环化反应同时发生。随后用LiAlH 4还原酯部分,得到(+)-四氢鸟啶,(+)-tashiromine,(1 S从市售起始原料仅在六个步骤中,分别以4.9%,4.1%,3.0%和5.9%的总收率得到,8a R)-1-(羟甲基)八氢吲哚嗪和(+)-癫痫素。