base component of a number of pyrrolizidine alkaloids. This necine subunit is an amino triol bearing a primary allylic alcohol characterized by an all-cis relationship of its stereocenters. The synthesis of (+)-crotanecine has been accomplished in 10 steps and 10.2% overall yield. The key step in the asymmetric synthesis is a Lewis acid-promoted, tandem inter[4 + 2]/intra[3 + 2] cycloaddition between
(+)-Crotanecine (1) 是许多
吡咯里西啶
生物碱的 necine 碱成分。该 necine 亚基是带有伯
烯丙醇的
氨基三醇,其特征在于其立体中心的全顺式关系。(+)-crotanecine 的合成分 10 步完成,总产率为 10.2%。不对称合成中的关键步骤是(富马酰氧基)硝基烯烃 14 和手性 β-甲
硅烷基
乙烯基醚 (-)-26 之间的
路易斯酸促进的串联 [4 + 2] / [3 + 2] 内环加成。该合成用于说明串联环加成的合成多功能性以引入额外的功能。