Synthesis of Highly Substituted 3‐Formylfurans by a Gold(I)‐Catalyzed Oxidation/1,2‐Alkynyl Migration/Cyclization Cascade

3‐Formylfuran derivatives are core structures of a variety of bioactive natural products. However, procedures for their preparation are still rare and generally inefficient in terms of atom economy: These methods require multiple steps or harsh reaction conditions and show selectivity problems. An efficient gold(I)‐catalyzed cascade reaction that leads to 3‐formylfurans from easily accessible starting materials is now described. A wide variety of 3‐formylfurans were obtained from the corresponding symmetric and unsymmetric 1,4‐diyn‐3‐ols in the presence of an N ‐oxide in good to excellent yields. Isotope‐labeling experiments as well as DFT calculations support a mechanism in which, after an initial oxygen transfer, a 1,2‐alkynyl migration is favored over a hydride shift; a cyclization ensues to afford the desired functionalized furan core.