1.4 chiral diamine building block

The resulting 1,3-dinitro compounds with two consecutive stereochemically defined stereocenters can be readily converted into the corresponding 1,3-diamines, which are versatile chiral building blocks from synthetic as well as pharmaceutical viewpoints (Scheme 9.19). 

The configurationally robust [CpRe(NO)(PPh3)X] complexes, easily obtained in an enantiomerically pure form (except for X = OR, NR2), were used as building blocks for new chiral hgands with spectator chiral-at-metal fragments. Both chiral diphosphine (117) and diamine ligands (118) have been prepared and successfully tested in catalysis. ... 

Asymmetric hydrogenation of bromo-substituted aromatic a-enamides 14 affords the corresponding bromo-amino acid derivatives 15, which subsequently is subjected to Pd-catalyzed cross-coupling with aryl and vinyl boronic acids. In addition to diverse phenylalanine derivatives 16, a broad array of other novel aromatic and heterocyclic amino acids have been produced rapidly from a small number of bromo-functionalized intermediates [24], This same two-step process may be applied to the production of many other classes of aromatic and heterocyclic chiral building blocks, such as arylalkylamines, amino alcohols, diamines, and directly on peptides as well. 

Finally, reaction E in Fig. 4 illustrates a stereoselective synthesis that proceeds by differentiation of two enantiotopically related groups of a meso compound. Here, one hydroxyl group of d.s-1,2-cyclohexanediol is preferentially benzoylated in the presence of one molar equivalent of an enantiomerically pure diamine [26]. These desymmetrization reactions (that have many biological versions) are also called meso-tricks , and are currently receiving a great deal of attention for the preparation of new chiral building blocks [27]. 

The simple primary-tertiary diamine salts can be successfully applied in the aldol reactions of a-hydroxyketones with good activity and excellent stereoselectivity. Notably, the catalyst enabled the reaction of dihydroxyacetone (DHA), a versatile C3-building block in the chemical and enzymatic synthesis of carbonhydrates. By employing either free or protected DHA, syn- or anh-diols could be selectively formed with excellent enantioselectivity (Scheme 5.7). Since enantiomers of diamine 26 and 29 are readily available, this class of chiral primary amine catalysts thus functionally mimics four types of DHA aldolases in nature [17b]. Later, simple chiral primary-tertiary diamine 27 derived from amino acid was also found to be a viable catalyst for the iyn-selective aldol reactions of hydroxyacetone and free DHA (Scheme 5.7) [18]. 

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