The aerial part of Dittrichia viscosa is an important renewable source of isocostic acid 1 which was isolated in gram-scale.  This isocostic acid 1 is an appropriate starting material for a rapid and efficient synthesis of new eudesmane acids 3,4-epoxy-α-eudesma-12-oic acid 2b, 3-oxo-4-dehydroeudesma-12-oic acid 4b, and known eudesmane acids viscic acid 5b, β-isocostic acid 6b, 3,5,11(13)-trieneudesma-12-oic acid 7b and 5-α-hydroxycostic acid 8b which were isolated from different plants with very low yields.