Synthetic approach for constructing the 1-oxygenated carbazole core and its application to the preparation of natural alkaloids

An efficient synthetic approach for the construction of the 1-oxygenated carbazole core is described. The condensation of cyclohexane-1,2-diones with a series of anilines yielded the corresponding 2-anilinocyclohex-2-en-1-ones, followed by the one-pot aromatization/methylation process of the latter to provide N-aryl-2-methoxyanilines. A palladium(II)-catalyzed cyclization of these N-aryl-2-methoxyanilines afforded the desired 1-methoxycarbazole frame in high overall yields. This protocol was implemented for the total synthesis of the naturally occurring glycozolicine and 6-methoxymurrayanine.