Cedrene isoprenologues

Cedrene isoprenologues In a detailed examination of the several varieties that constitute the E. georgei complex, two were found to produce diterpenes with a C5 extended cedrene skeleton, eg 173 (121,122). Nmdr and 2D-nmr measurements on this compound indicated the presence of a l-methyl-4,4,6-trisubstituted cyclohexene component which is not contained in the two other tricyclic diterptene skeletons, decipiane and eremanes, previously isolated from Eremophila species. 

Although a number of syntheses of cedrol and cedrenes have been achieved (72), extension of these to the synthesis of the cedrene isoprenologues requires the introduction of an extra asymmetric centre at C6. 

The cedrene isoprenologues can also be generated from the carbocation (213).which, in this case, alkylates the Si-face of CIO in a lOZ-ene. The spiro-ring system produced displays the 1,4-cis- disubstituted cyclopentane ring. Further cyclization of this intermediate generates the tricyclic ring system of the 2-ep/-cedrene metabolites as shown in Scheme 52. 

Although the sequences presented above are entirely hypothetical, they have proven useful in suggesting the type of skeleton that a newly discovered ring system might contain. This has been the case for the bisabolene isoprenologues and, more importantly, the cedrene isoprenologues. The intermediate role of this skeleton on the sequence leading to the eremanes is predictable. 

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