10.1055/s-0031-1290380
The research focuses on the development of an efficient synthetic route to 1-oxygenated carbazole alkaloids, which are key structural motifs in various biologically active alkaloids and pharmaceuticals. The study introduces an anionic [4+2] annulation of lithiated furoindolones with dimethyl maleate, followed by selective demethoxycarbonylation, to synthesize 3-methoxycarbonylcarbazoles. This method led to the straightforward synthesis of two natural products, clausine E and mukonine, as well as their 4-prenyl analogues. Additionally, the research uncovered a new route to cyclohepta[d,e,f]carbazole. The conclusions of the study highlight the potential of this annulation strategy for the synthesis of carbazole natural products and the discovery of an unprecedented cyclization leading to the formation of a cycloheptacarbazole motif.