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 α‐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 13 C‐labeling experiment, according to which an unprecedented chemoselective heterodimerization of two different isocyanides generates an α‐amidoketenimine intermediate, which undergoes 1,3‐amino migration to form an α‐imidoylketene, followed by 6 π electrocyclization.