A Concise, Stereocontrolled Total Synthesis of Rippertenol

Rippertenol and the kempane diterpenes are biogenetically derived from cembrene A and are dense with stereochemical complexity despite a paucity of heteroatom functionality. A discussion of past synthetic efforts towards these complex targets is presented to define the current level of understanding regarding the controlled synthesis of these molecules in order to place the studies described in Chapters 2 and 3 in better context. A unique tricyclic polyunsaturated ketone intermediate was synthesized as a platform from which to approach cycloaddition chemistry towards rippertenol. Efforts towards this novel intermediate, including a highly stereoselective conjugate addition to an unsaturated ketone and a demanding intramolecular aldol condensation, are described. An uncommon Lewis Acid-promoted inverse electron demand Diels-Alder reaction and a challenging ring expansion lead to the first laboratory total synthesis of rippertenol. The synthesis was completed in 19 total steps, 13 of which were necessary following the completion of a known starting material.