An Alkyne–Isocyanide Cycloaddition/Boulton-Katritzky Rearrangement/Ring Expansion Reaction: Access to 9‑Deazaguanines

An alkyne–isocyanide [3 + 2] cycloaddition followed by a Boulton–Katritzky rearrangement and a ring expansion is demonstrated. Different from the typical Boulton-Katritzky rearrangement, which forms five-membered ring products, the rearrangement-ring expansion method provides a mild, efficient, and atom-economical access to fused 9-deazaguanine structures in high yields.