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

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 alpha,beta-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.