Scope and Limitations of the Intermolecular Furan-Yne Cyclization

Different types of alkynes were reacted with 2,5-disubstituted furans in order to evaluate the scope of the intermolecular furan-yne reaction. With ethynyl aryl ethers as starting materials, 2-phenoxy phenols were accessible in moderate to good yields. A different reaction mode was observed for alkynes bearing electron-withdrawing substituents. For these starting materials a cis-selective hydroarylation took place in an anti-Markovnikov fashion in excellent yields. 1,2-Diynes turned out to be suitable starting materials as well. Due to the second alkynyl moiety, after an initial phenol synthesis, a subsequent hydroalkoxylation by the newly formed phenolic oxygen gives access to benzofurans in a tandem process.