Coleone C, D, I, I′ aus einer madegassischen Plectranthus sp. nov. Interkonversion von cis‐ und trans‐A/B‐6,7‐Diketoditerpenen

Coleons C, D, I, I′, obtained from a Madagascan Plectranthus sp. nov.. Interconversion of cis‐ and trans‐A/B‐6,7‐Diketoditerpenes. Fairly large amounts of Coleons C and D, as well as Coleons I and I′ (3‐O‐formyl derivative of Coleon I) can bc isolated from the orange glands of an unclassified North Madagascan Plectranthus sp. A reversible transformation of cis‐ and trans‐A/B‐6,7‐dioxo‐abietane via its diosphenol has been achieved for the first time. CD.‐Spectra of these compounds are presented. Hydrogenolysis of Coleon D leads to 6β,16‐dihydroxy‐royleanone.