Decarboxylative Grob-Type Fragmentations in the Synthesis of Trisubstituted Z Olefins: Application to Peloruside A, Discodermolide, and Epothilone D

Discriminating elimination: A new method for the synthesis of methyl-branched trisubstituted Z olefins, a structural motif in many polyketides with anticancer activity, relies on an ⁻OH-induced decarboxylative Grob-type fragmentation (see scheme; Ms=mesyl). The starting materials are β-mesyloxy lactones with a quaternary α center, which are prepared by aldol reactions in a diastereo- and enantioselective manner.