via a Mannich base to the nitrile 17 (Scheme 7) which in turn is cyclized to the Preininger‐alkaloid (2b) by careful hydrogenation. ‐ Reduction of 2b with a modified Iwakuma‐reagent, followed by N‐formylation and subsequent LiAlH4‐reduction produced (R)‐(+)‐macrostomine (enantiomer of 1) in 72% optical purity.
Preininger-
生物碱,脱氢-normacrostomine(2b,方案1)是从rac开始合成的。α-乙酰基-3,4-二甲氧基苄基
氰(3)(方案2)。关键中间体 4-乙酰基-6,7-二甲氧基-1-(3,4-亚甲基-二氧苄基)
异喹啉(11)通过曼尼希碱转化为腈17(方案7),腈17又环化为Preininger -
生物碱 (2b) 小心氢化。- 用改良的 Iwakuma - 试剂还原 2b,然后进行 N - 甲酰化和随后的 LiAlH4 - 还原,以 72% 的光学纯度生成 (R) - (+) - macrostomine(1 的对映异构体)。