An approach to the bicyclic C-5-C-17/C-19-C-20 (BC) portion of neoclerodane diterpenes by intramolecular Diels-Alder reaction

Using a highly diastereoselective intramolecular acrylate [4+2] cycloaddition as the key step, a short route from 3-furaldehyde to a bicyclic building block for the synthesis of neoclerodane diterpenes was developed. A first attempt featuring a conjugate methylation of a dienyl lactone failed, but a streamlined sequence using an all-encompassing intramolecular Diels-Alder reaction of a sterically congested 1,3-diene was successful. A highly diastereoselective intramolecular acrylate [4+2] cycloaddition of a sterically congested 1,3-diene served as the key step in a short synthesis of a BC building block for neoclerodane diterpenes.