Silver-Catalyzed Chemoselective [4+2] Annulation of Two Isocyanides: A General Route to Pyridone-Fused Carbo- and Heterocycles

A silver-catalyzed chemoselective [4+2] annulation of aryl and heteroaryl isocyanides with -substituted isocyanoacetamides was developed for the facile and efficient synthesis of 2-aminoquinolones, naphthyridines, and phenanthrolines. A mechanism for this multistep domino reaction is proposed on the basis of a C-13-labeling experiment, according to which an unprecedented chemoselective heterodimerization of two different isocyanides generates an -amidoketenimine intermediate, which undergoes 1,3-amino migration to form an -imidoylketene, followed by 6 pi electrocyclization.