Total Synthesis of (±)- and (−)-Actinophyllic Acid
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- 作者：Connor L. Martin ; Larry E. Overman ; Jason M. Rohde
- 刊名：Journal of the American Chemical Society
- 出版年：2010
- 出版时间：April 7, 2010
- 年：2010
- 卷：132
- 期：13
- 页码：4894-4906
- 全文大小：661K
- 年卷期：v.132,no.13(April 7, 2010)
- ISSN：1520-5126
文摘
Development of efficient sequences for the total syntheses of (±)-actinophyllic acid (rac-1) and (−)-actinophyllic acid (1) are described. The central step in these syntheses is the aza-Cope/Mannich reaction, which constructs the previously unknown hexacyclic ring system of actinophyllic acid in one step from much simpler tetracyclic precursors. The tetracyclic hexahydro-1,5-methano-1H-azocino[4,3-b]indole ketone rac-37 is assembled from o-nitrophenylacetic acid in four steps, with oxidative cyclization of a dienolate derivative of tricyclic precursor rac-35 being the central step. In the first-generation synthesis, this intermediate is transformed in two steps to homoallyl amine rac-43, whose formaldiminium derivative undergoes efficient aza-Cope/Mannich reaction to give pentacyclic ketone rac-44. In four additional steps, this intermediate is advanced to (±)-actinophyllic acid. The synthesis is streamlined by elaborating ketone rac-37 to β-hydroxyester intermediate rac-53, which is directly transformed to (±)-actinophyllic acid upon exposure to HCl and paraformaldehyde. This concise second-generation total synthesis of (±)-actinophyllic acid is realized in 22% overall yield from commercially available di-tert-butyl malonate and o-nitrophenylacetic acid by a sequence that proceeds by way of only six isolated intermediates. The first enantioselective total synthesis of (−)-actinophyllic acid (1) is accomplished by this direct sequence from tricyclic keto malonate (S)-35. Catalytic enantioselective reduction of α,β-unsaturated ketone 66 is the key step in the preparation of intermediate (S)-35 from the commercially available Boc-amino acid 65. Discussed also is the possibility that the aza-Cope/Mannich reaction might be involved in the biosynthesis of (−)-actinophyllic acid.