Abstract The first total synthesis of a member of the helioporin class of marine diterpenes has been achieved. Starting from (4a S)-η 6-5,6-dimethoxytetralin-Cr(CO) 3 (≥99% e.e.) the target molecule (putative helioporin D) is obtained in a mere 8 steps in an excellent overall yield of 45%. The synthesis is based on the specific reactivity and stereochemistry of the arene-Cr(CO) 3 substructure and involves highly regio- and diastereoselective benzylic deprotonation / alkylation steps. The 6-methyl-5-hepten-2-yl sidechain is diastereoselectively introduced in a stereoconvergent manner by alkylation of a benzylic lithiated complex with the in situ generated triflate of ( R)-6-methyl-5-hepten-2-ol. The relative configuration of the alkylation product was confirmed by X-ray crystal structure analysis. As the NMR data of the synthetic target compound are not in agreement with those of natural helioporin D, the stereostructure of the latter has to be revised.