A short route to functionalized imidazo[4,5-c]carbazoles. Synthesis of the first example of the imidazo[4,5-c]β-carboline ring system

A new synthetic route to functionalized imidazo[4,5-c]carbazoles (4) via intramolecular electrocyclization of indolo-1,3,5-hexatriene system (3a) is described. Thermally induced ring-closure of 2-ethylcarboxylate-(4-amino-5-imidazolyl)-3-indole (3d) led to the previously unknown imidazo[4,5-c]β-carboline ring system (5). These heterocycles were efficiently converted into analogs of both the marine cytotoxic agents grossularines-1 and -2 (1) and the antimicrobial alkaloid eudistomin U (2).