A new route to 1-oxygenated carbazoles. Synthesis of the carbazole alkaloids murrayafoline-A and murrayaquinone-A

Abstract

1-Oxygenated carbazoles are prepared in 4 steps from indole-2-carboxylates by condensation with γ-butyrolactones to give the lactones (12), followed by hydrolysis with concomitant decarboxylation to the alcohols (13), and oxidation to the aldehydes (14). The aldehydes (14) cyclise to 1-methoxycarbazoles on treatment with boron trifluoride–methanol or with methanolic hydrogen chloride. The methoxycarbazoles (15a) and (4) were converted into the corresponding carbazolequinones (18) and (7) by demethylation, and oxidation. The carbazole alkaloids murrayafoline-A (4) and murrayaquinone-A (7) were prepared.