A novel synthetic route for the total synthesis of (±)-uleine

New Route to 20-Deethyldasycarpidone by Ring-Closure with DDQ

“…The required N-methyl{2, 3,4,9-tetrahydrospiro[1H-carbazole-1,2 -(1,3)dithiolane]-2-yl}-2-acetamide (5) was prepared by the activation of 4 as the mixed anhydride with ethyl chloroformate and triethylamine in chloroform, followed by the addition of 40% aqueous methylamine. 2,3-Dichloro-5,6-dicyanobenzoquinone (DDQ) was then used for the facile cyclization [18][19][20][21][22][23] to the azocino[4,3-b]indole skeleton 6 and subsequent conversion to 20-deethyldasycarpidone (8). The most characteristic absorption of its 1 H-NMR spectrum of 6 is a broad doublet of the methine hydrogen at the C-21 position at δ 4.53 which is comparable to the data observed previously for the analogous methanoazocino [4,3-b]indole structure.…”

A DFT Investigation on the Structure, Spectroscopy (FT‐IR and NMR), Donor‐Acceptor Interactions and Non‐Linear Optic Properties of (±)‐1,2‐Dehydroaspidospermidine

“…Addition, these alkaloids have been attracted considerable interest by synthetic chemists due to the unique challenges posed by their structural features, i. e., their pentacyclic framework, as well as their potent pharmacological properties. Therefore, the synthetic chemists commonly have looked for the new strategy to produce these natural compounds with highly efficiently . The results of a recent study of dehydroaspidospermidine indicated that the strychnos‐type indole compound could be synthesized by Fischer cyclization with a highly‐effective synthetic process, but it is quite challenging .…”

“…Therefore, the synthetic chemists commonly have looked for the new strategy to produce these natural compounds with highly efficiently. [10][11][12][13][14] The results of a recent study of dehydroaspidospermidine indicated that the strychnos-type indole compound could be synthesized by Fischer cyclization with a highly-effective synthetic process, but it is quite challenging. [15] However, the synthesis of as an intermediate agent was reported without an investigation and discussion of the electronic and spectroscopic because such an investigation was not a part of the scope of that study.…”

Facile synthesis of the azocino[4,3-b]indole framework of strychnopivotine and other Strychnos alkaloids

“…Previously we reported the synthesis of the azocino[4,3-b]-indole skeleton via the acid-catalyzed, [30][31][32] as well as oxidative cyclization (oxidant 2,3-dichloro-5,6-dicyanobenzoquinone) 33-35 from appropriate 2-substituted 1-oxo-1,2,3,4-tetrahydrocarbazole derivatives, the ring closure taking place at position 4 of the carbazole ring. As an alternative, herein, we report a new protocol for the cyclization of a 4-substituted 1-oxo-1,2,3,4-tetrahydrocarbazole, leading to the desired 1,5-methanoazocino[4,3-b]-indole structure in a 45% overall yield over six steps involving the D ring closure by NaH-promoted aldol reaction (Scheme 1).…”