Cyclic monoterpenoids limonene

Finally the biotransformation of limonene was carried out with the same microorganism in the same fashion as with geraniol and nerol. The details of this research will be discussed in the chapter of cyclic monoterpenoids (1.2.1). 

Allylic alcohols [e.g. citronellol, geraniol (8), and nerol (18)] exhibit strong shielding at the y-carbon and deshielding at the 5-carbon in the 13C n.m.r. upon acylation.127 Cationic exchange resins separate acyclic [e.g. myrcene (12)] from cyclic (e.g. limonene) monoterpenoids.128... 

Further dissociation and cyclization by electrophilic addition of the cationic carbon to the terminal double bond then gives a cyclic cation, which might either rearrange, undergo a hydride shift, be captured by a nucleophile, or be deprotonated to give any of the several hundred known monoterpenoids. As just one example, limonene, a monoterpenoid found in many citms oils, arises by the biosynthetic pathway shown in Figure 27.10. 

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