Synthesis of cyclopenta[b]indol-1-ones and carbazol-4-ones from N-(2-halophenyl)-substituted enaminones by intramolecular Heck reaction

An efficient synthetic route towards N-methylated or nonmethylated 3,4-dihydrocyclopent[b]indol-1(2H)-ones (3) and 1,2,3 9-tetrahydrocarbazol-4(4 H)-one (10) was elaborated, based on Pd-catalyzed intramolecular Heck reaction. The chemoselectivity of the cyclization was studied in the case of the bi- and trifunctional substrates 12 and 17, respectively. In the latter case, depending on the catalyst, either the brominated indole 18 or the tetracyclic compound 19 were obtained by single and double Heck reaction, respectively.