A chiral pool approach for asymmetric syntheses of (-)-antrocin, (+)-asperolide C, and (-)-trans-ozic acid

Ozonolysis of aromatic abietane (+)-carnosic acid (4) is used to create an important intermediate in an enantiomerically pure form, resulting in a simple, concise, readily scalable, and asymmetric synthesis of (-)-antrocin (1). This strategy not only provides an efficient approach to (-)-antrocin (1) synthesis but can also be readily adopted for the syntheses of optically pure (+)-asperolide C (2) and (-)-trans-ozic acid (3) from the naturally abundant aromatic abietanes (+)-podocarpic acid (5) and (+)-dehydroabietic acid (6). The strategy presented here is an example of the use of naturally occurring aromatic abietanes as a chiral pool and offers an account of the asymmetric synthesis of terpenoids.