Catalytic Enantioselective Total Synthesis of Riccardiphenol B

The first catalytic enantioselective total synthesis of riccardiphenol B, a sesquiterpene derivative isolated from a Japanese collection of the liver-wort Riccardia crassa, has been achieved. A copper-catalyzed asymmetric conjugate addition of trimethylaluminum was used at an early stage to generate the quaternary stereogenic center with high enantiomeric excess. The corresponding sterically en-cumbered aluminum enolate was directly trapped with an alpha-amino ether, allowing after oxidation, the release of a key intermediate in the total synthesis of the target natural product.