Catalytic C-H Functionalization Driven by CO as a Stoichiometric Reductant - Application to Carbazole Synthesis

Significance A general synthetic method for carbazole, thieno[2,3- b ]indole and 9 H -Pyrido[2,3- b ]indoles by palladium-catalyzed CO-mediated reductive cyclization of 2-nitro biaryls compounds is reported. The reactions proceed in excelled yields under mild conditions. Comprehensive screening of conditions shows that conversion is increased with increasing temperature and pressure, with optimal conditions being 70 psi of CO and 140 °C in DMF utilizing 2 mol% of Pd(OAc) 2 and 4 mol% of ligand (1,10-phenanthroline). A broad range of heterocycles has been prepared by this method.