Mulberry Diels−Alder Adducts: Synthesis of Chalcomoracin and Mulberrofuran C Methyl Ethers

Abstract

The synthesis of each of the heptamethyl ethers of the mulberry Diels−Alder adducts chalcomoracin (1) and mulberrofuran J (2) is described. The key steps in each approach involved a biomimetic intermolecular [4+2]-cycloaddition between a dehydroprenylphenol diene derived from an isoprenoid-substituted phenolic compound and an α,β-unsaturated alkene of a chalcone as the dienophile. Critical to the success of the Diels−Alder reaction was the presence of the free phenol in the 2′-hydroxychalcone