Phosphine-catalyzed [3+2] Annulations of γ-functionalized Butynoates and 1C,3O-bisnucleophiles: Highly Selective Reagent-controlled Pathways to Polysubstituted Furans

In this paper, a reagent-controlled [3+2] annulation of γ-functionalized butynoates 1 and 1C,3O-bisnucleophiles 2 is reported, which leads to three distinct furan skeletons 3-5. A PPh(3) catalyst preferentially attached the β-position of 1a, facilitating α-addition to furnish Type I annulations. With the assistance of Ag(2)O, Type II annulations were achieved via selective γ-substitution. In the absence of the PPh(3) catalyst, the reagent Cs(2)CO(3) promoted β-addition to realize Type III annulations.