Monoterpene chiral pool

All the optically active terpenes mentioned in this chapter are commercially available in bulk (>kg) quantities and are fairly inexpensive. Although many of them are isolated from natural sources, they can also be produced economically by synthetic methods. Actually, two thirds of these monoterpenes sold in the market today are manufactured by synthetic or semi-synthetic routes. These optically active molecules usually possess simple carbocyclic rings with one or two stereo-genic centers and have modest functionality for convenient structural manipulations. These unique features render them attractive as chiral pool materials for synthesis of optically active fine chemicals or pharmaceuticals. Industrial applications of these terpenes as chiral auxiliaries, chiral synthons, and chiral reagents have increased significantly in recent years. The expansion of the chiral pool into terpenes will continue with the increase in complexity and chirality of new drug candidates in the research and development pipeline of pharmaceutical companies. 

The variety of terpenes is great but they may not be available in high ee. Here is a selection these are all monoterpenes (C10) and may be linear, cyclic or bicyclic. We have included the new chiral pool members 8-phenyl-menthol 83 and camphorsulfonic acid 94. 

An interesting variation on the use of chiral amine auxiliaries was reported by Taillades.30 This group took advantage of the chiral pool and transformed optically active monoterpene 50 into amino-based chiral auxiliary 51. Exposure of 51 to 8 ultimately gave rise to 52. 

---