Derived from Other Amino Alcohols

Ephedrine and prolinol are the most common compounds employed to prepare P-stereogenie oxazaphospholidines. In spite of that, other 1,2-amino aleohols 

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The most successful of the Lewis acid catalysts are oxazaborolidines prepared from chiral amino alcohols and boranes. These compounds lead to enantioselective reduction of acetophenone by an external reductant, usually diborane. The chiral environment established in the complex leads to facial selectivity. The most widely known example of these reagents is derived from the amino acid proline. Several other examples of this type of reagent have been developed, and these will be discussed more completely in Section 5.2 of part B. 

Among the ethers of prolinol, (5)-2-methoxymethylpyrrolidinc [SMP, (S)-10] has found most applications. It is readily prepared from prolinol by the normal sodium hydride/iodo-methane technique9,13 (sec also Section 2.3. for O-alkylations of other amino alcohols) and is also commercially available. An improved synthesis from proline avoids the isolation of intermediates and gives the product (which is highly soluble in water) by continuous extraction14. SMP has been used as the lithium salt in deprotonation and elimination reactions (Section C.) and as an auxiliary for the formation of chiral amides with carboxylic acids, which in turn can undergo carbanionic reactions (Sections D.l.3.1.4., D.l. 1.1.2.. D.l. 1.1.3.1., in the latter experimental procedures for the formation of amides can be found). Other important derivatives are the enamines of SMP which are frequently used for further alkylation reactions via enolates (Sections D.l.1.2.2.. where experimental procedures for the formation of enamines are... 

In addition to the amino acid derived amino alcohols mentioned above, two other amino alcohols have been widely used ( R, 25)-ephedrine (8) which is a naturally occurring plant alkaloid, and the (5, 5)-amino diol (9) which is produced microbiologically as a byproduct from the manufacture of the antibiotic chloramphenicol. Note the presence of two adjacent [or contiguous] stereogenic centres in both these molecules, a useful feature also present in two of the amino acids, (5,5)-isoleucine (10) and (25,3/ )-threonine (11). The (/ )-amino alcohol (12) is also readily available in enantiomerically pure form. 

In addition, these authors have reported the synthesis of other A -sulfony-lated amino alcohols derived from camphor that have been examined as ligands... 

The other phospholipids can be derived from phosphatidates (residue = phosphatidyl). Their phosphate residues are esterified with the hydroxyl group of an amino alcohol choline, ethanolamine, or serine) or with the cyclohexane derivative myo-inositol. Phosphatidylcholine is shown here as an example of this type of compound. When two phosphatidyl residues are linked with one glycerol, the result is cardiolipin (not shown), a phospholipid that is characteristic of the inner mitochondrial membrane. Lysophospholipids arise from phospholipids by enzymatic cleavage of an acyl residue. The hemolytic effect of bee and snake venoms is due in part to this reaction. 

It has recently been shown that when the tetrahedral intermediate of the reaction is cyclic, it is a better donor of nucleophilic CF3. These cyclic intermediates can be generated intramolecularly from trifluoroacetamides or trifluorosulfmamides derived from (9-silylated ephedrine. These reagents are able to trifluoromethylate aldehydes and ketones, even in the case of enolizable substrates, as a strong base is not required (Figure 2.34). However, while the source of CF3 is chiral, there is no chirality transfer to the addition product, and the replacement of ephedrine by other chiral amino alcohols did not show any improvement. " Similar to asymmetric trifluoromethylation with the Ruppert reagent, only the use of a fluoride salt of cinchonine can increase the enantioselectivity. " " ... 

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