Novel oxidopyrylium-alkene [5+2] cycloaddition conjugate addition cascade (C<sup>3</sup>) sequences are reported. Readily accessible via Grubbs-Hoveyda cross-metathesis, a variety of acetoxypyranone-alkenes with pendant nucleophiles undergo [5+2] cycloaddition followed by conjugate addition from the concave face of the intermediate pyranone toward bridged, tetracyclic ethers. In some cases, 3 new rings, 4 new bonds, and 6 new contiguous stereocenters were constructed with excellent diastereoselectivity. Finally, an asynchronous concerted reaction pathway is proposed to explain the high diastereoselectivity of the oxidopyrylium-alkene [5+2] C<sup>3</sup>.

Surprising organic synthesis: Serendipitous discovery of a novel cascade process

249th National Meeting (2015)

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