Synthesis of 5- and 6-Azaindoles by Sequential Site-Selective Palladium-Catalyzed C–C and C–N Coupling Reactions

Two-step sequential procedures for the Pd-catalyzed synthesis of 5- and 6-azaindoles are reported. The reactions proceed in very good yields. 6-Azaindoles are formed through site-selective Pd-catalyzed Sonogashira reaction of 3,4-dibromopyridine with alkynes, followed by a Pd-catalyzed tandem C–N coupling and cyclization with amines. On the other hand, 5-azaindoles are obtained by a site-selective Pd-catalyzed C–N coupling reaction of 3,4-dibromopyridine with amines, followed by C–C coupling and cyclization with alkynes.