Synthesis of Cyclobutanones by Gold(I)-Catalyzed [2 + 2] Cycloaddition of Ynol Ethers with Alkenes

A broad scope synthesis of cyclobutanones by gold(I)-catalyzed [2 + 2] cycloaddition of ynol ethers with alkenes has been developed. We also found that internal aryl ynol ethers can undergo (4 + 2) cycloaddition reaction with alkenes leading to the corresponding chromanes.