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.