Studies on the synthesis of the azocino[4,3‐b]indole framework and related compounds

Abstract

An efficient method for the synthesis of C-4 position alkylated azocino [4,3-b]indole 13 and 18 is described. Reduction of compounds 5, 6, 7 and 8 yielded the corresponding alcohols. Compounds 5, 6, 7 and 8 were synthesized through several steps starting from 1. The resulting alcohols underwent acid catalyzed ring closure to give tetracyclic azocino [4,3-b]indole 9, 10, 11 and 12. Finally, compounds 9 and 17 were alkylated at C-4 position to the corresponding products 13 and 18. The structure of the compounds 13 and 18 has been confirmed by X-ray single crystal analysis.

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.…”

Studies on the synthesis of 4‐oxo‐2,3,4,9‐tetrahydrocarbazole derivatives

“…Unfortunately, cyclization of compounds 12 and 13 under a variety of conditions failed. Compounds 14 and 15 were never detected [2–5] (Scheme ).…”

“…Recently we reported the total synthesis of (±)‐epidasycarpidone [1] based on the acid catalyzed D‐ring cyclization of the appropriate 4‐oxo‐1,2,3,4‐tetrahydrocarbazol derivative. 4‐Oxotetrahydrocarbazole with a functionalized ethyl side chain plays an important role in the synthesis of the hexahydroazocino[4,3‐ b ]indole frame work [2–5]. In the present work, the synthesis of 2‐ethyl‐substituted 4‐oxo‐tetrahydrocarbazole derivatives is described.…”

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 .…”