Cyclic terpenes, functional groups

The only other functional group is the conjugated unsaturated ester. This functionality is remote from the stereocenters and the ketone functionality, and does not play a key role in most of the reported syntheses. Most of the syntheses use cyclic starting materials. Those in Schemes 13.4 and 13.5 lead back to a para-substituted aromatic ether. The syntheses in Schemes 13.7 and 13.8 begin with an accessible terpene intermediate. The syntheses in Schemes 13.10 and 13.11 start with cyclohexenone. Scheme 13.3 presents a retrosynthetic analysis leading to the key intermediates used for the syntheses in... 

Using methylene-triphenylphosphorane 205, in many cases carbonyl functions have been converted into exomethylene groups in cyclic terpene chemistry. This technique was used, among others in the preparation of (+)-steviol methyl ether 244), dihydro-5,6-norcaryophyllene 245), ( )-nootkatone 246 (-)-phyllodadene 247), and (+)-e-cadinene 248). In the synthesis of the latter the trans-decalin derivative 462 was formed from the cis-decalone 461 the epimerization of which proceeded via the enol form during the methylenation 248 (Scheme 80). 

Most terpene structures can be broken down into multiples of isoprene units. Terpenes contain various functional groups (C=C, OH, C=0) as part of their structures and may be acyclic or cyclic. 

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