Synthesis of Methylenecyclobutenes by [2+2] Cycloaddition of Allene Ethers and Alkyne

Methylenecyclobutenes are useful precursors to provide other organic compounds. We report intermolecular [2+2] cycloaddition of allene ethers and alkynes at 100 degrees C, which gives methylenecyclobutenes in 50-60 % yields. The reaction does not require any metal catalyst and shows broad substrate scope, high regioselectivity and high stereoselectivity. Methylenecyclobutenes are synthesized via thermal conditions between allene ethers and alkyne and successfully transformed to other four-membered ring compounds. This strategy provides a series of methylenecyclobutenes in moderate yields with broad functional groups. image