RESUMO
The first enantioselective total syntheses of (-)-pallambinsâ A-D have been achieved in 15 or 16 steps from a known chiral cyclohexenone. Salient features of the syntheses include a palladium-catalyzed oxidative cyclization to assemble the [3.2.1]bicyclic moiety, an Eschenmoser-Claisen rearrangement/lactone formation sequence to construct the Câ ring, an intramolecular Wittig reaction to form the Dâ ring, and individual transformations of pallambinsâ C and D to generate pallambinsâ A and B. The described synthesis avoids protecting-group manipulations through the design of highly chemo- and stereoselective transformations. During the course of this work, a palladium-catalyzed method for the dehydrobromination of α-bromoketones was developed, and the scope of this transformation was also investigated.