Chiral synthesis of the necic acid components, crobarbatic acid and integerrinecic acid lactone

Samarium(II) diiodide-promoted regioselective fragmentation of the γ-halogeno esters 12 and 13 afforded the olefins 14 and 20, respectively, which were converted into the necic acid components, crobarbatic acid and a known advanced intermediate of integerrinecic acid lactone, of macropyrrolizidine alkaloids.