Amines, absolute configuration

Fluorescamine has been used as a Cottonogenic reagent for secondary amines (forming aminoendione chromophore)275 and for primary amines (forming pyrrolinone chro-mophore, 107)276 whose in situ CD was directly correlated with the amine absolute configuration. 

Nitrogen chirality may also be produced by the action of an achiral peroxyacid on a Schiff base containing a chiral amine (75JOC3878). In this case the oxaziridine contains a configurationally known centre of chirality relative to this, absolute configurations of the centres of chirality at nitrogen and carbon, and thus the complete absolute configuration of the molecule, can be determined (see Section 5.08.2.2). 

Compounds analogous to the cobaltammines may be similarly obtained using chelating amines such as ethythenediamine or bipyridyl, and these too have played an important role in stereochemical studies. Thus ct5-[Co(cn)2(NH3)Cl] was resolved into d(+) and /(—) optical i.so-mers by Werner in 1911 thereby demonstrating. to all but the most determined doubters, its octahedral stereochemistry. More recently, the absolute configuration of one of the optical isomers of [Co(en)3] was determined (.sec Panel on p, 1125),... 

The absolute configuration of amine 3 is not specified. Additional information is not available. 

IR spectra, 2,469 protonation, 2, 465 zinc transport, 6, 672 Citric acid, fluoro-absolute configuration, 2, 478 Citric add, hydroxy-crystal structure, 2, 478 Clathrates amines, 2,25... 

NMR can be a powerful tool for determination of enantiomeric excess or absolute configuration of the optically active compounds, however, these processes require the use of some auxiliaries, for example, chiral lanthanide shift reagents or chiral derivatising agent. In many cases, the starting point for determination of enantiopurity of amines, amino acids or diols is the formation of chiral imines. 

In determination of the absolute configuration of a-chiral primary amines, BINOL derivatives were used as chiral derivatizing agent.10 In this procedure, the chiral substrate was derivatized with R and S enantiomers of the 2,-methoxy-l,l -binaphthalene-8-carbaldehyde and the XH spectra of both diastereomers were compared. Comparison of the chemical shift differences of the diastereomers has allowed determination of the absolute configuration of the chiral substrate [5]. 

Perez-Fuertes et al.6 8 have suggested the possibility of using the three-component chiral derivatizing approach for prediction of the absolute configuration of amines. Comparison of aH NMR spectra has shown significantly more deshielded signals of (S,S)-imino-boronate esters, derivative of a-amino esters than (S,R) diastereomers. 

The absolute configuration of the chiral center in the 1-boraadamantane moiety was established by X-ray analysis of (S,S) 57 on the basis of the known stereo-structure of the chiral amine ligand. 

The focus of the earlier chapter was a brief outline of the sources of chiral amino compounds, application of Brewster s rules for the assignment of the absolute configurations to a few chiral amines, a discussion of the ORD and CD in the visible (380-780 nm) and near-ultraviolet (200-380 nm) spectral regions of chiral amino compounds and some of their derivatives, and how the observed Cotton effects (CEs) in their ORD curves and CD spectra relate to their conformational preferences and absolute configurations. 

The absolute configuration of primary amines containing the chiral centre at the a-position has been correlated with the relative H shifts (upheld or downfield) observed in the NMR spectra of the amides formed with (5 )-0-methylmandelic acid, PhCH(0Me)C02H316. 

From the examples cited above, it is evident that a great deal of research remains to be done on the chiral-amine-catalyzed Michael reaction. All mechanistic proposals have been based solely on knowledge of the absolute configuration of the products, while kinetic data as well as steric factors have not been carefully delineated. Since the research thus far has been restricted entirely to products in which just one chiral center is formed, it is clear that there is no lack of problems to be studied. 

The 36d-LAH complex was applied to the reduction of ketone oximes and their O-tetrahydropyranyl and O-methyl derivatives to optically active amines (69). Results for a variety of phenyl alkyl and dialkyl ketones are shown in Table 4. The predominant amines formed all were of the S absolute configuration with optical purities up to 56%. The oxime hydroxy group presumably reacts with the less hindered H2 in the 36d-LAH complex (cf. Scheme 6) to form an oxime complex (45), which probably undergoes infermolecular hydride transfert of H2 from a second molecule of the 36d-LAH complex (Scheme 8). Asymmetric reduction with the ethanol-modified 36d-LAH reagent gave amines of R con-... 

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