Regiospecific Synthesis of Mono-N-substituted Indolopyrrolocarbazoles

<UFIGR ID="ol051550an00002">Two complementary and efficient strategies have been developed for the regiospecific synthesis of unsymmetrical indolopyrrolocarbazoles (IPCs) mono-N-substituted with a pentacycle. A halogen in position 2 of the intermediate bisindolylmaleimides <BO>3a</BO>−<BO>e</BO> allows a selective Mitsunobu coupling by exploiting the increased acidity of the 2-chloro-substituted indole nitrogen. It also promotes an easier cyclization of bisindolylmaleimides <BO>4a</BO>−<BO>e</BO> and <BO>7b</BO>−<BO>e</BO> to IPCs. Alkylation of the 2-unsubstituted indole-3-carboxamides <BO>2a</BO>,<BO>b</BO> and further processing to the corresponding IPCs gives access to the opposite regioisomers.