A novel approach to a formal total synthesis of the monoterpenoid indole alkaloid (±)-tangutorine has been developed starting from an α,β-unsaturated cyclic dehydroamino ester. Synthesis of the rather unusual trans-substituted 2,3-indoloquinolizidine substructure was accomplished viaCu(II)-mediated conjugate addition and organozinc/copper coupling as the key steps, thereby setting the stage for ring-closing metathesis to produce the quinolone substructure. Finally, Bischler–Napieralski cyclization gave rise to the pentacyclic system of (±)-tangutorine thereby realizing a formal synthesis in an overall yield of 5.2% in eight consecutive steps.
从 α、β-不饱和环状脱氢
氨基酯开始,我们开发了一种正式全合成单萜
吲哚生物碱 (±)- 唐古丁的新方法。通过
铜(II)介导的共轭加成和
有机锌/
铜偶联作为关键步骤,合成了相当不寻常的反式取代 2,3-
吲哚喹嗪亚结构,从而为闭环偏析生成
喹啉酮亚结构创造了条件。最后,Bischler-Napieralski 环化反应产生了 (±)- 唐古丁的五环系统,从而实现了正式合成,通过八个连续步骤,总收率达到 5.2%。