Monoterpenes skeletal structure

Fig. 6-2. Skeletal structures of several monoterpenes that have been identified in the atmosphere.

The tens of thousands of known C15 terpenes derive from farnesyl pyrophosphate (5), which can be cyclized to produce about 300 different skeletal structures. The majority of known sesquiterpenes have been isolated from fungi, marine organisms and Streptomyces species, but a large number are also produced by flowering plants, where they serve a variety of functions. Like monoterpenes, many are found as components of essential oils. Other sesquiterpenes function as insect attractants, antifeedants or phytoalexins. 

Rearrangements of Iboga and Aspidosperma Types. It is possible to envisage the biological rearrangements of the monoterpene-tryptamine alkaloid skeleta as proceeding via a common intermediate (132), reversibly derivable, at least on paper (see below) from each of the skeletal types, providing that a structure at the correct oxidation level is chosen. Thus tabersonine (133) (aspidosperma). 

In 1899, Wagner published The Strueture of Camphene, in which he challenged the accepted structure of the bicyclic monoterpene camphene that had been proposed by his contemporaries. He stipulated that the acid-catalyzed dehydration of bomeol (1) resulted from a skeletal rearrangement to give camphene (2), a structure unique from its precursor. 

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