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.