Nitrogen asymmetric

A successful case study for asymmetric nitrogen oxidation was reported for a series of (hetero)aromatic tertiary amines. High diastereoselectivity was observed for the enzyme-mediated oxidation of S-(—)-nicotine by isolated CHMOAdneto to give the corresponding ds-N-oxide [215]. The stereoselectivity of this biooxidation was complementary to the product obtained by flavin M O (FM O) from human li ver (trows-selective [216]) as well as unspecific oxidations by FMOs from porcine and guinea pig liver. 

Coordination of ammonia or a substituted ammonia to a metal ion alters markedly the N — H dissociation rate (see See. 6.4.2). Since also proton dissoeiation of complexed ammines is base-catalyzed, then exchange can be made quite slow in an aeid medium. Thus, in a eoordinated system of the type 12, containing an asymmetric nitrogen atom (and this is the only potential souree of optical activity), there is every chance for a successful resolution in acid conditions, since inversion is expected only after deprotonation. It was not until 1966 that this was suc-eessfully performed, however, using the complex ion 12. A number of Co(III), Pt(II) and Pt(IV) complexes containing sarcosine or secondary amines have been resolved and their raeemizations studied.Asymmetrie nitrogen centers appear eonfined to d and d ... 

Molecules which contain a chiral cobalt as well as an asymmetric nitrogen exist in four possible optical isomeric forms. These are represented for Co(sar)(hbg) +, hbg = NH2C( = NH)NHC(=NH)NH2 in Fig. 7.12. All four optically-active isomers have been isolated and characterized by cd, nmr and vis/uv absorption spectroscopy. The kinetics of... 

The coordination chemistry of macrocyclic ligands has been extensively studied and aspects of isomerism have been considered in numerous systems.241 Methods whereby two diastereomers of complexes of tetra- N-methylcyclam may be isolated have been discussed previously.184 This, however, is a relatively simple system and it is usually necessary to consider isomerism due to the presence of asymmetric atoms in the chelate arms, as well as that due to asymmetric donor atoms that may be rendered stable to inversion by coordination. An example of a system exhibiting this level of complexity is afforded by the nickel(II) complexes of the macrocyclic ligands generated by reduction of the readily prepared macrocycle (46). These ligands contain two asymmetric carbon atoms and four asymmetric nitrogen atoms but, because AT-inversion is rapid, it is conventional to consider that only three separable stereoisomers exist. There is an enantiomeric pair, (47a) and (47b), which constitutes the racemic isomer (R, R ), and an achiral (R, S ) diastereomer (47c), the meso isomer. 

FIGURE 5.41 Molecular models showing diastereomers of the A-sym-cis-R,R-cdda complex with respect to the absolute configurations of the coordinated asymmetric nitrogens and the normal axial (a) and abnormal equatorial (b) orientations of the terminal acetate rings. The solid circles in (a) refer to the acetate and the cyclohexane methylene of which the protons suffer severe steric contact as shown by arrows.170... 

Asymmetric Nitrogen Transfer with Nitrido-manganese Complexes... 

Since a chiral nitride complex is considered to be a good candidate for an asymmetric nitrogen transfer reagent, the intention of the authors group was to apply some complexes to asymmetric organic synthesis [22]. 

Quaternary ammonium salts with asymmetric nitrogen atoms. Inversion of configuration is not possible because there is no lone pair to undergo nitrogen inversion. For example, the methyl ethyl isopropyl anilinium salts can be resolved into enantiomers. 

Rudchcnko. V. F.. Ignatov, S. M., Chervin, 1.1., Nosova, V. S and Kostyanovskii, R. G Asymmetric nitrogen. XLVll. Geminal systems. XXXI. Dialkoxyamines synthesis, hydroxy- and aminomethylation, NMR spectra, configurational stability, hv. Akad. Nauk SSSR Ser. Khim., 1153, 1986 Chem. Ahstr., 106, 175847, 1987. 

The chiral nitridomanganese complex 545 represents a novel self-contained asymmetric nitrogen-transfer reagent which has been used to convert alkenes to scalemic aziridines directly, although a stoichiometric amount of transfer reagent is required. This protocol makes use of A -2-(trimethylsilyl)ethanesulfonyl chloride (SESCl) (546) as an activator, providing A -SES-aziridines 547 that are easily deprotected under mild conditions using... 

Diaziridines differ from simple amines and hydrazines radically in many properties. First of all, the nitrogen atoms of diaziridines feature high pyramidal stability. The inversion of nitrogen atoms in diaziridine rings has been studied actively since 1967 <67CB1778>. Optically active diaziridines with an asymmetric nitrogen atom have been studied since 1974 <74izvi67i>. In the molecules of... 

Asymmetric Influence from the trans Ligand. As shown later, when an asymmetric nitrogen is in the trans position of the complexes of the type trans N,//)-[PtCl(L-am)(ethylene)], asymmetry is introduced by the substitution of tbn for the ethylene in organic solvents. 10.) L-Alanine, L-phenylalanine, and L-valine fail to introduce asymmetry on the incoming tbn in the equilibrated state. However, L-proline, N- and C-substituted L-proline and even -substituted L-valine induce asymmetry. (Table V) There must be some electronic interaction from the asymmetric nitrogen upon the olefin through platinum(II). 

Figure 12 also shows the projection of this Zeise-type complex the C-C moiety is placed across the square plane of platinum(II) behind the paper. A common contribution of the minus region to the lower left behind the paper seems to predominate for the Zeise-type and the present complexes. The d-IT transition may be perturbed by the asymmetric nitrogen trans to ethylene to give a marked CD peak in this region. 

---