Total Synthesis of Carbazole Alkaloids – Ekeberginine, Harmandianamine A, and Furanoclausamine B

Abstract

The anionic [4 + 2] annulation of 3‐substituted furoindolones with dimethyl maleate provides an expedient route for the synthesis of the title carbazole alkaloids. The employment of this strategy in combination with a Krapcho reaction/retro‐Kolbe–Schmitt reaction has culminated in the first total synthesis of the lactonic carbazoles harmandianamine A and furanoclausamine B and a brief total synthesis of ekeberginine from a prenylated furoindolone. An unusual fragmentation of an ester function during the annulation is also reported.

Regiodefined synthesis of brominated hydroxyanthraquinones related to proisocrinins

“…Subsequent O -methylation of 20 (using CH 3 I, K 2 CO 3 ), and benzylic bromination of 21 with NBS followed by lactonization of 22 in a refluxing mixture of dioxane and water afforded phthalide 23 in 61% yield. NBS bromination of 23 afforded the 3-bromophthalide [ 33 ], which on treatment with dioxane/water furnished phthalaldehydic acid 24 in 69% yield over two steps [ 34 ]. Treatment of 24 with KCN furnished 3-cyanophathalide 12 in 75% yield analogously as described in references [ 35 – 37 ].…”

Procedure for the Synthesis of Polysubstituted Carbazoles from 3-Vinyl Indoles

“…Many carbazole-containing molecules exhibit a wide range of biological activities, such as antiviral, antimalarial, anti-TB activity, and antitumoral properties . Carbazole moieties are also found in many natural compounds . Furthermore, because of their wide band gap and high luminescence efficiency, carbazoles are excellent building blocks for functional materials, especially materials used in organic light-emitting diodes (OLEDs) .…”