The unnatural enantiomer of the alkaloid codonopsinine was prepared employing a suitably substituted alkoxyallene equipped with a D-fructose-derived auxiliary. The crucial lithiated 1-alkoxy-3-arylallene was generated in situ from easily available 1,2:4,5-di-O-isopropylidene-3-O-[3-(4-methoxyphenyl)-1,2-dien-1-yl]-β-D-fructopyranose and treated with an N-tosyl imine to afford a diastereomeric mixture of the corresponding allenyl adducts. Their cyclization with silver nitrate in acetonitrile in the presence of potassium carbonate furnished highly substituted 2,5-dihydropyrrole derivatives. After separation, straightforward synthetic operations, with highly diastereoselective hydroborations as key step, provided (+)-codonopsinine (≥95% ee) and one of its stereoisomers.

中文翻译：

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党参碱非天然对映异构体和烷氧基丙二烯立体异构体的不对称合成

生物碱党参碱的非天然对映异构体是使用配备有 D-果糖衍生辅助剂的适当取代的烷氧基丙二烯制备的。关键的锂化 1-烷氧基-3-芳基丙二烯是从易于获得的 1,2:4,5-二-O-异亚丙基-3- O- [3-(4-甲氧基苯基)-1,2-二烯- 1-基] -β -D-吡喃果糖并用N-甲苯磺酰亚胺以提供相应联烯基加合物的非对映异构体混合物。在碳酸钾存在下，它们在乙腈中与硝酸银环化，得到高度取代的 2,5-二氢吡咯衍生物。分离后，直接合成操作，以高度非对映选择性硼氢化反应为关键步骤，提供 (+)-党参碱 (≥95% ee) 及其立体异构体之一。