Gold(I)‐Catalyzed Ring Expansion of Alkynylcyclopropyl Allyl Ethers to Construct Tetrasubstituted Methylenecyclobutanones: A Mechanistic Investigation about the Character of Catalytic Amount of Water

Abstract A gold(I)‐catalyzed ring expansion of alkynylcyclopropyl allyl ethers to produce tetrasubstituted methylenecyclobutanones in moderate to good yields has been disclosed in this paper. This reaction proceeded through an intramolecular [3,3]‐sigmatropic rearrangement followed by [1,2]‐allyl shift pathway in the presence of catalytic amount of water upon gold(I) catalysis. The intriguing reaction mechanism has been proposed on the basis of deuterium and 18 O‐labeling experiments, Mass spectroscopic analysis, 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopic tracking and density functional theory (DFT) calculations. The further transformation of these methylenecyclobutanones into polycyclic skeleton has been realized by a practical three‐step synthetic procedure. Several other transformations have been also indicated. magnified image