Lateral Lithiation-Initiated Annulations in the Synthesis of 1-Oxygenated Carbazole Alkaloids and a Cycloheptacarbazole

Anionic [4+2] annulation of lithiated furoindolones with dimethyl maleate followed by selective demethoxycarbonylation provides an efficient synthetic route to 3-methoxycarbonylcarbazoles. The route has led to the straightforward synthesis of two natural products, namely clausine E, mukonine, and their 4-prenyl analogues. A new route to cyclohepta[ d , e , f ]carbazole was also uncovered during the investigations.