An Alternative Synthetic Access to cis-4a-Methyloctahydrophenanthrene, a Biomarker of Sergipe-Alagoas Basin Petroleum in Brazil

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.