A Metal-Free Tandem C-C/C-O Bond Formation Approach to Diversely Functionalized Tetrasubstituted Furans

A novel and efficient method for the synthesis of diversely functionalized furans is developed via DBU-mediated tandem Michael addition/5-exo-dig-cycloisomerization of enynes and keto-methylenes. This [3 + 2]-annulation is operationally simple under metal-free reaction conditions with 100% atom economy and broad substrate scope.