Stereocomplementary Routes to Hydroxylated Nitrogen Heterocycles: Total Syntheses of Casuarine, Australine, and 7-<i>epi</i>-Australine
作者:Camilla Parmeggiani、Francesca Cardona、Leonardo Giusti、Hans-Ulrich Reissig、Andrea Goti
DOI:10.1002/chem.201301320
日期:2013.8.5
occurred with perfect diastereoselectivity furnishing a bicyclic 1,2‐oxazine derivative, which is an excellent precursor for pyrrolizidine alkaloids hydroxylated at C‐7 with optional configuration at this stereogenic center. Depending on the stage of the NO bond cleavage and ring re‐closure, 7‐hydroxypyrrolizidines with 7R or 7S configuration were obtained, as a result of completely selective addition reactions
向D-阿拉伯糖衍生的环状硝酮中添加锂化的1-苄氧基丙二烯具有完美的非对映选择性,从而提供了双环1,2-恶嗪衍生物,这是在C-7处羟基化的吡咯并烷生物碱的极佳前体,在该立体异构中心具有可选构型。根据内环C底部或顶部互补发生的完全选择加成反应的结果,根据NO键断裂和环重新闭合的阶段,获得了具有7 R或7 S构型的7-羟基吡咯烷核苷六元和五元B环中的C双键。这些有效的立体异构途径可用于获得多羟基吡咯烷核生物碱,这是通过木麻黄碱和奥沙林的有效合成证明的,这是两类不同构型的7-羟基吡咯烷核生物碱的实例。australine的替代性合成和7-制备两种策略外延-australine也报道,这表明,氢化物还原环外的C的立体选择性 Ô双键独立于环的大小,从顶面优先发生六元或五元环。