cis-4a-Methyloctahydrophenanthrene (1) was prepared in 8 steps (23% overall yield) from 2-bromophenyl)acetic acid (3) and cyclohexane-1,3-dione (6). A highly cis-diastereoselective Michael-type Heck coupling served as the key step in the assembly of the tricyclic skeleton. This compound 1 was used as gas chromatography standard which allowed the unequivocal identification of a minor biomarker present in Carmopolis oil from the Sergipe-Alagoas Basin in Brazil.135664668