Stereoselective synthesis of (±)-β-elemene by a doubly diastereodifferentiating internal alkylation: a remarkable difference in the rate of enolization between syn and anti esters

A total synthesis of the sesquiterpene (±)-β-elemene (1) has been achieved starting from a simple acyclic precursor 4. Key transformations include a ‘doubly diastereodifferentiating folding and allylic strain-controlled’ intramolecular ester enolate alkylation. In the course of the synthesis, we encountered remarkably different reactivity between syn and anti diastereomeric esters in the enolization step.