Synthesis of Tricyclic Fused 3-Aminopyridines through Intramolecular Co-I-Catalyzed [2+2+2] Cycloaddition between Ynamides, Nitriles, and Alkynes

The first [2+2+2] cocyclizations between ynamides, nitriles. and alkynes are reported. They open a new access to unprecedented nitrogen-containing heterocycles of type 2-trimethylsilyl-3-aminopyridines. Such frameworks, which can be found in various compounds of biological interest, are very difficult to prepare by conventional methods. However. using [CpCo(C2H4)(2)] (Cp = cyclopentadienyl) as catalyst, the intramolecular cyclizations could be achieved in up to 100% yield. The presence of the trimethylsilyl group allowed a rare type of Hiyama cross-coupling: one of the silylated pyridines could be coupled with p-iodoanisole to give a new type of biaryl system.