Total Synthesis of Pallamolides A−E

Abstract

We have achieved the first total synthesis of pallamolides A‐E, of which pallamolides B‐E possess intriguing tetracyclic skeletons with novel intramolecular transesterifications. Key transformations include highly diastereoselective sequential Michael additions to construct the bicyclo[2.2.2]octane core with simultaneous generation of two quaternary carbon centers, a one‐pot SmI2‐mediated intramolecular ketyl‐enoate cyclization/ketone reduction to generate the key oxabicyclo[3.3.1]nonane moiety, and an acid‐mediated deprotection/oxa‐Michael addition/β‐hydroxy elimination cascade sequence to assemble pallamolides tetracyclic skeletons. Kinetic resolution of ketone 14 via Corey‐Bakshi‐Shibata reduction enabled the asymmetric synthesis of pallamolides A‐E.