and Annulation of Enones. Enantiocontrolled Total Synthesis of (-)-Retigeranic Acid

Article abstract of DOI:10.1021/ja00199a032

The lithium dienolates of ethyl 2-bromocrotonate and of other, more highly substituted α-bromocrotonates underwent smooth addition to enones to provide, in one step, the corresponding vinylcyclopropanes in excellent yields.The vinylcyclopropanes were subjected to several modes of rearrangement: thermolysis to afford annulated cyclopentenes in an overall <2 + 3> annulation sequence; conversion to enol ethers to give, via the Cope rearrangement of divinylcyclopropanes, bicyclo<3.2.n> systems; and nucleophilic opening with trimethylsilyl iodide to afford, at lowtemperatures, intermediate allylic iodides that were cyclized to annulated cyclopentenes under basic conditions.The stereochemical details of the vinylcyclopropanation and the cyclopentene rearrangement were investigated.The application of this process was realized by the convergent and enantiocontrolled total synthesis of (-)-retigeranic acid.The scope, the limitation, and some future applications of this methodology are indicated.