Synthesis of the Spirochroman Core of Dihypoestoxide and Stereochemical Proposal for the Natural Product

The tricyclic spirochroman core of dihypoestoxide has been synthesized from geranoic acid in seven steps using a hetero-Diels-Alder cycloaddition as a key step, thus providing support for the proposed biosynthesis of the natural product. Furthermore, analysis of the C-13 NMR data obtained for all four diastereoisomers of the synthetic spirochroman core has allowed us to propose a full stereochemical assignment for dihypoestoxide.