128 



TERPENOIDS AND STEROIDS 



Most of the monocyclic sesquiterpenoids have the skeleton shown below with variations 

 in double bond location and functional groups. Some examples of this type are shown in 

 Table 5. 



There are other more unusual monocyclic structures found among the sesquiterpe- 

 noids. Some of these cannot be conveniently constructed from isoprene residues. Pre- 

 sumably rearrangements and oxidation play a part in their formation from isoprenoid 

 precursors. A few examples are given in Table 6. 



Most of the bicyclic sesquiterpenoids can be divided into naphthalene types and 

 azulene types according to which of these two aromatic structures they give on dehydro- 

 genation. Further subdivision takes into account the locations of substituent groups on 

 the rings. Low temperature distillation may be sufficient to convert some azulenogenic 

 terpenoids into azulenes, and it is generally believed that the azulenes themselves never 

 occur in nature, although this is open to some question (7, 8, 9). 



Napthalenic: 



eudalene type 



cadalene type 



Azulenic: 



guaiazulene type vetivazulene type 



Some specific examples are shown in Table 7. 



zierazulene type 



