Guaiane-type sesquiterpenes

Transannular cyclizations of cyclodecadiene monoepoxides have been studied in exhaustive detail, particularly amongst natural germacranolides, because of their relevance to biogenetic models for the synthesis of eudesmane- and guaiane-type sesquiterpenes. " A full discussion of this topic is beyond the scope of this chapter, but the examples collected in equations (54-64) provide the reader with an in-... 

Some very interesting results have been obtained by Henderson et al who have used micro-analytical techniques in conjunction with electron- and photomicroscopy to determine the sites of sesquiterpene accumulation in Pogostemon cablin (rich in guaiane-type sesquiterpene hydrocarbons). The results of this study indicate that there are specific sites of accumulation especially associated with the glandular trichomes of the second pair of primordial leaves, where the concentration of sesquiterpenes is twelve-fold relative to other parts of the plant. 

We have already mentioned our approach to guaiane-type sesquiterpenes, by ring expansion of simple monoterpenes, followed by annulations of the five-membered ring [30-33]. The annulation chemistry can be planned with allylation, Wacker reaction and subsequent aldol reaction [102], or Grignard chemistry followed by RCM [103]. Scheme 64 illustrates these results. 

Two New Guaiane-type Sesquiterpene Lactones and Their Related Sesquiterpene Lactones from Porella japonica. Phytochem. 20, 257 (1981). 

Suzuki, M Kowata, N Kobayashi, H., and Tanaka, I. (1990) The structure of germacrane-type sesquiterpene alcohol, a possible precursor of the guaiane-type sesquiterpene from the brown alga Dictyopteris divaricata. Chem. Lett., 2187-2190. 

The africanane sesquiterpenes have an interesting rearranged guaiane-type carbon skeleton, which can be obtained from (/ )-pulegone, ring contraction, side chain elaboration, and RCM (Scheme 24) [59]. 

Proazulenes, azulenogens, hydroazulenes a group of natural cyclic sesquiterpenes, which can be terminally dehydrogenated or dehydrated to Azulenes (see). P. are chiefly compounds of the guaiane type, e.g. guaiol. 

Ishii, H., T. Tozyo, and H. Minato Structure of Liguloxide, Liguloxidol, and Liguloxidol Acetate, Sesquiterpenes of Antipodal Guaiane Type. Chem. Commun. 1968, 106. 

Guaiane sesquiterpenes, which are not formed by the same biosynthetic pathway as the types of sesquiterpenes found in the pungent Lactarius species (Scheme 1), can be considered chemotaxonomic markers of species belonging to Section Dapetes. The latter mushrooms are characterized by the secretion of a strongly colored milky juice and are usually edible and of pleasant taste (2). 

Fig. 8.1.12. Some important sesquiterpene types based on guaiane cation...

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