Chiral Synthesis of a Pyrrolizidine Alkaloid, (-)-Heliotridane

Abstract

Chual synthesis of the necic base, heliotridane has been achieved by employing a samarium diiodide-promoted regioselective carbon-carbon bond cleavage reaction of the y-halo ester (17), as a key step.Recently we developed samarium(I1) diiodide-promoted carbon-carbon bond cleavage reaction of y-halo carbonyl compoundsl and this novel fragmentation reaction was expected to have broad utility in the synthesis of natural products.In the continuation of a research program to exploit this synthetic strategy in the natural products synthesis,2,3 we planned the synthesis of pymolizidine alkaloids, and here report a chual synthesis of the necic base, heliotridane (I), in natural enantiomeric form, together with a stereoselective synthesis of pseudoheliotridane (2).