Amines configuration determination

Based on the CCM system described above, an enantioselective version thereof was presented by Togni and coworkers a decade later [9]. The use of a new class of catalyst precursors led to substantially improved reactivity, and the system now was truly catalytic, with turnover frequency (TOP) values reaching up to 3.37 h at 348 K (Equation 6.5 Table 6.1). The absolute configuration of the resultant amine was determined by internal comparison of the X-ray crystal structure of the... 

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 SnI reactions do not proceed at bridgehead carbons in [2.2.1] bicyclic systems (p. 397) because planar carbocations cannot form at these carbons. However, carbanions not stabilized by resonance are probably not planar SeI reactions should readily occur with this type of substrate. This is the case. Indeed, the question of carbanion stracture is intimately tied into the problem of the stereochemistry of the SeI reaction. If a carbanion is planar, racemization should occur. If it is pyramidal and can hold its structure, the result should be retention of configuration. On the other hand, even a pyramidal carbanion will give racemization if it cannot hold its structure, that is, if there is pyramidal inversion as with amines (p. 129). Unfortunately, the only carbanions that can be studied easily are those stabilized by resonance, which makes them planar, as expected (p. 233). For simple alkyl carbanions, the main approach to determining structure has been to study the stereochemistry of SeI reactions rather than the other way around. What is found is almost always racemization. Whether this is caused by planar carbanions or by oscillating pyramidal carbanions is not known. In either case, racemization occurs whenever a carbanion is completely free or is symmetrically solvated. 

The current work indicates that sulfided platinum catalysts are, in general, more active and selective than Pt, Pd, or sulfided Pd catalysts for reductive alkylation of primary amines with ketones. The choice of the catalyst preparation parameters, especially the support, plays a major role in determining the performance of the catalyst. Diamines, especially of lower molecular weight, tend to react with ketones even at room temperature to form heterocycles such as imidazolidine, diazepanes, and pyrimidines. Hence, a continuous reactor configuration that minimizes the contact between the amine and the ketone, along with a highly active catalyst is desired to obtain the dialkylated product. In general, sulfided Pt appears to be more suited for the reductive alkylation of ethylenediamine while unsulfided Pd or Pt may also be used if 1,3-diaminopropane is the amine. 

The silyl ketene acetal rearrangement can also be carried out by reaction of the ester with a silyl triflate and tertiary amine, without formation of the ester enolate. Optimum results are obtained with bulky silyl triflates and amines, e.g., f-butyldimethylsilyl triflate and (V-methyl-Af, /V-dicyclohcxylaminc. Under these conditions the reaction is stereoselective for the Z-silyl ketene acetal and the stereochemistry of the allylic double bond determines the syn or anti configuration of the product.243... 

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]. 

The configurations of bis-aminals 68 were determined by analysis of 13C NMR data <2002T5733>. One-, and two-dimensional homo-, and heteronuclear studies ( H, 13C, H- H COSY, HMQC, and HMBC) were conducted for the first time to determine the structures of three stereoisomeric 2-methylperhydro-93-azaphenalcnc alkaloids 45 <1999MRC60>. Complete assignment of H and 13C NMR spectra of compound 86, which is a derivative of 3, has been reported <2002T5733>. The 13C NMR spectrum of compound 98 is consistent with a Cz symmetry <1996JOC4125>. 

A method for the determination of the absolute configuration of chiral primary amines of type 1 has been developed on this basis251. The amines 1 are converted via sulfonamides 2 into... 

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