Cascade Benzannulation Approach for the Syntheses of Lipocarbazoles, Carbazomycins, and Related Alkaloids.

Herein, a state-of-the-art one-pot cascade benzannulation technique for the efficacious synthesis of valuable 3-hydroxy-2-methyl carbazoles, a linchpin of more than 25 carbazole-based alkaloids, is unveiled from readily affordable fundamental commodities. The key step of this strategy is gaining aromaticity by site-selective elimination of hydroxyl group controlled by nucleophilicity of the indole ring. The present strategy shows excellent functional group tolerance with a broad substrate scope. The utility of this convenient approach was appealingly exemplified via concise total syntheses of 10 carbazole-based alkaloids possessing significant biological activities and thus of medicinal importance.