An Efficient Stereoselective Synthesis of a Tricyclic Intermediate for the Synthesis of Derivatives of Abietic and Podocarpic Acids

For many years the synthesis of diterpene acids has attracted the attention of organic chemists. Kröniger and Wheeler 1 reported that the condensation of the dimethylate 1a with methyl malonate gave the cis compound 2a which on heating with palladised charcoal was converted into the trans isomer 3a . Compound 3a is a promising intermediate in the synthesis of derivatives of both abietic and podocarpic acids, while 2a could be a starting material for the synthesis of cis fused diterpene acids. However, the route to 2a and 3a was inefficient; 1a was only available as the minor component of a mixture with its epimer 1b ; and the yield for the stage 2a + 3a was poor.