13 BIOMIMETIC REACTION OF GERMACRENE-TYPE SESQUITERPENES
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From a biogenetic point of view, many sesquiterpenes are considered to be derived from germacrenes or germacrones as an important precurser, and their conformations have been discussed in connection with their transannular reactions as well as with thermal isomeizations. Thus, molecular mechanics calculations were successfully carried out to evaluate relative stabilities of each conformation of several germacrenes in their ground states and transition states. Particularly, molecular mechanics calculation was carried out successfully in the case of thermal reaction of acoragermacrone, and also attempted for the acid-catalyzed reaction of preisocalamendiol leading to the formation of isocalamendiol, although the result so far obtained was not necessarily satisfied. On the basis of the above results, acid and base-catalyzed reactions of epoxygermacrene-D were carried out to give many interesting compounds similar to oppositol, axisonitrile-1, periplanone-A, junenol and so on. Reaction process of these compounds is also presented.
