Palladium(II)-catalyzed intramolecular carboxypalladation-olefin insertion cascade: direct access to indeno[1,2-b]furan-2-ones.

A catalytic, atom-economical, domino 5-endo-dig cyclization-intramolecular olefin insertion sequence was developed under mild conditions. Aryl alkynoic acids bearing a tethered enone partner afforded the indeno[1,2-b]furan-2-ones, the core skeleton present in a number of biologically significant molecules including the natural product solanacol, under ligand-free, palladium-catalyzed reaction conditions in high yields. The competitive β-hydride elimination in the final step leading to the conjugated analogs was avoided by the addition of lithium bromide. A plausible mechanism for this domino sequence is proposed involving intramolecular carboxypalladation and olefin insertion steps.