Synthesis of fused polycyclic nitrogen-containing heterocycles via cascade cyclization

A novel strategy for the synthesis of fused polycyclic-nitrogen containing heterocycles via cascade cyclization is described. The methodology involves condensation of 1-(2-aminophenyl)-9H-β-carboline-3-carboxylic acid amide with isothiocyanates followed by in situ treatment of the resulting thioureas with HgCl2 for 1 h at rt. The one-pot cascade cyclization leads to interesting changes in molecular structure and an increase in molecular complexity. A mechanistic rationale for the cascade cyclization is discussed.