Synthesis of Furo[2,3-b]pyran-2-ones through Ag(I)- or Ag(I)-Au(I)-Catalyzed Cascade Annulation of Alkynols and α-Ketoesters.

Ag(I)- or Ag(I)-Au(I)-catalyzed cascade annulation of alkynols (5-hexyn-1-ol systems) with α-ketoesters involving a dual activation process (π and σ) has been developed for the first time. This reaction proceeds through cycloisomerization of alkynol to give the 6-endo-enol ether followed by annulation with an α-ketoester to furnish furo[2,3-b]pyran-2-ones in good yields. Chemical structures of all products were rigorously confirmed by single crystal X-ray analysis and analogy.