Cyclization of 2-Alkynylallyl Alcohols to Highly Substituted Furans by Gold(I)-Carbene Complexes

Various 2-alkynylallyl alcohols were synthesized by a generally applicable Sonogashira coupling protocol. Subsequent gold-catalyzed transformation was investigated. The use of Au-I catalysts bearing carbene ligands, of either the N-heterocyclic carbene or nitrogen acyclic carbene type, delivered the desired products with low catalyst loadings and under very mild reaction conditions. A broad array of substrates was tested, including alkyl-, alkenyl-, and aryl-substituted alkynes, as well as substrates with two alkynyl moieties. The methodology turned out to have a broad scope. Secondary allyl alcohols were also tolerated, and the resulting trisubstituted furans could be isolated in high yields.