Synthesis of the key intermediate(±)-18,19-dinor-14αH-cheilantha-12,15-dien-17-one and its transformation into the geochemical marker 18,19-dinor-13βH, 14αH-cheilanthane and the marine-type sesterterpene methyl scalar-17-en-25-oate

Abstract

(±)-Methyl isocopalate (1) was converted into 18,19-dinor-14αH-cheilantha-12,15-dien-17-one (5). This key intermediate was then used as starting material for the synthesis of the tricyclane 18,19-dinor-13βH,14αH-cheilanthane (6) and its C-13 epimer (19). The hydrocarbon (6) is the most abundant member of a series of biological markers from petroleums and sediments. Starting from (5) the sesterterpene of marine-type scalar-17-en-25-oate (8) through the tricyclic esters (21) was also synthesized. The (Z) isomer of (21) possesses the carbon skeleton of the fern sesterterpene cheilanthatriol (10).