New chiral building blocks from

Kolbe electrolysis of trilfuoromethylated carboxylic acids has been shown to be a versatile method for providing useful building blocks having a CF3 group. Seebach and Renaud have prepared new types of trifluoromethylated chiral building blocks from enantiomerically pure 3-hydroxy-4,4,4-trifluorobutyric acid (Scheme 7.6) [76]. 

The new chiral building block (23) has been obtained by lipase-catalysed hydrolysis of the corresponding meso-diacetate, which was itself prepared from ribitol monoester (23) was converted in three steps into the lactone (24), which has been reported to have hunger-modulating properties. 

Figure 5.21 Cyanohydrins are precursors for hydroxyamino acids, amino acids and amino alcohols. New sol-gel CACHy catalysts convert aldehydes and ketones into such valued chiral building blocks. (Reproduced from Avecia.com, with permission.)...

Optically active EP is an important C3 chiral building block for the synthesis of chiral pharmaceuticals such as j9-adrenergic blockers [11 -13], vitamins [14,15], pheromones [16], natural products [17], and new materials such as ferro-electric crystals [18]. Racemic EP can be made via 2,3-DCP and l,3-dichloro-2-pro-panol (1,3-DCP) synthesized from propylene by organic synthesis [19] however, a practical production method for optically active EP has not yet been established. Racemic 2,3-DCP, which is easily synthesized by the chemical... 

We conclude this section with two examples of the synthesis of chiral products by starting from an appropriate chiral building block. This has been named the chiron approach by Hanessian, and is described in great detail in his book.t l The distinctive feature of this type of reaction is that no new stereogenic units are formed and all the stereogenic units of the product are directly derived from the starting material. For this reason these cannot be considered as asymmetric synthesis but methods of this type are of some practical importance in areas where suitable chiral starting materials are readily available. 

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