ABSTRACT
The efficient synthesis of chiral natural products, synthons, and drugs using palladium metal complexes as catalysts is currently a great challenge for modern synthetic chemistry, due to its well-known economic and ecological advantages. The palladium reactivity toward a given catalytic reaction can be adjusted by the coordination of donor ligands to the metal center. The ligand properties are a combination of the donor atom nature with the backbone structure, which is frequently of great importance for stereo-inductive effects in asymmetric reactions. Particularly, palladium-catalyzed decarboxylative asymmetric allylic alkylation is a reliable approach to generate quaternary stereocenters. The stereochemical outcome with preferential formation of stereoisomer supports a trans-oxypalladation process via a chair-like intermediate B. The chiral chroman 49, containing a quaternary carbon stereogenic center, was obtained with 80% yield and an enantiomeric excess higher than 99%. A similar palladium-catalyzed intramolecular alkoxycarbonylation reaction has been reported as one of the key steps in the total synthesis of (+)-monocerin.
