Divergent Access\nto Polycyclic Fluorenofuran Systems\nvia Palladium-Catalyzed Cascade Furan-Participated Diels–Alder\nCycloaddition Reactions

The\nPd-catalyzed reaction of 1-(2-iodophenyl)-3-arylprop-2-yn-1-ones\nwith benzene-tethered furan-ynes produces novel fused hexacyclic indenone-furan\nscaffolds, while the reaction with propargyl furfuryl ethers affords\nthe pentacyclic indenone-spirodifuran system. The thiophene-containing\nalkynes also proceed by similar transformations. A mechanism involving\nthe Pd-catalyzed coupling and propargylic Alder-ene reaction to generate\nthe indenone-allene intermediate, followed by an intramolecular furan/thiophene-participated\ninverse electron-demand Diels–Alder reaction, is proposed.