Pd(II)-catalyzed C–H annulation and lactonization of indole-2-carboxamides with hydroxyalkynoates using air as an oxidant

<h2>Abstract</h2> A novel palladium(II) catalyzed C–H annulation strategy has been developed for the synthesis of a diverse range of furo[3′,4':5,6]pyrido[3,4-<i>b</i>]indole-1,5(3<i>H</i>)-dione scaffolds. This is the first report on the construction of polycyclic carboline frameworks from indole-2-carboxamides and 4-hydroxy-2-alkynoates. This method provides a direct access to fused carbolines that are closely resemble to biologically active <i>β</i>-carboline frameworks.