De Novo Construction of Highly Substituted Chromones and Benzo[b]furans via a Switchable Transformation of 3-Alkynyl-4-pyrones with Active Methylene Compounds

A switchable ring-opening reaction of 3-alkynyl-4-pyrones with CH2-active compounds in basic medium has been developed for the efficient de novo synthesis of highly substituted benzofurans and chromones. The best selectivity is achieved under solvent-free conditions for the formation of chromones and in the presence of CuI for the formation of benzofurans. Both conditions are very mild and scalable. A large number of products bearing electron-withdrawing groups have been prepared in good to excellent yields.