Stereo differentiation

A chiral vanadium complex, bis(3-(heptafluorobutyryl)camphorato)oxovana-dium(IV), can catalyze the cycloaddition reaction of, mainly, benzaldehyde with dienes of the Danishefsky type with moderate to good enantioselectivity [21]. A thorough investigation was performed with benzaldehyde and different activated dienes, and reactions involving double stereo differentiation using a chiral aldehyde. 

Most asymmetric induction processes with Chital auxiliaries involve a stereo-differentiating reaction that affords one diastereomet as the primary product To obtain the desired enantiomer, the Chiral auxiliary must be removed Highly dia-stereoselective reactions between otganocoppet reagents and allylic substrates with... 

Figure 15.7 Cliromatographic separation of cliiral hydroxy acids from Pseudomonas aeruginosa without (a) and with (h) co-injection of racemic standards. Peak identification is as follows 1, 3-hydroxy decanoic acid, methyl ester 2, 3-hydroxy dodecanoic acid, methyl ester 3, 2-hydroxy dodecanoic acid, methyl ester. Adapted from Journal of High Resolution Chromatography, 18, A. Kaunzinger et al., Stereo differentiation and simultaneous analysis of 2- and 3-hydroxyalkanoic acids from hiomemhranes hy multidimensional gas cliromatog-raphy , pp. 191 -193, 1995, with permission from Wiley-VCH. (continuedp. 419)...

Izumi, Y. Tai, A. Stereo-differentiating Reactions p. 137 Academic Press, New York... 

Shorter chain analogs of DPPC were also investigated in order to determine if the lack of stereo-differentiation in monolayer properties could be due to DPPC s higher gel point or complicating steric effects. Figure 15 shows the compression/expansion isotherms of DPPC as compared with racemic and enantiomeric dimyristoylphosphatidyl choline (DMPC) and dilauroyl phosphatidyl choline (DLPC). Again no stereodifferentiation in monolayer properties was observed as reflected by 11/A isotherms or dynamic surface tension. 

Given the information above, the question remains as to the nature of the monolayer states responsible for the stereo-differentiation of surface properties in racemic and enantiomeric films. Although associations in the crystalline phases are clearly differentiated by stereochemical packing, and therefore reflected in the thermodynamic and physical properties of the crystals, there is no indication that the same differentiations occur in a highly ordered, two-dimensional array of molecules on a water surface. However, it will be seen below (pp. 107-127) that conformational forces that are readily apparent in X-ray and molecular models for several diastereomeric surfactants provide a solid basis for interpreting their monolayer behavior. 

As described hitherto, diastereoselectivity is controlled by the stereogenic center present in the starting material (intramolecular chiral induction). If these chiral substrates are hydrogenated with a chiral catalyst, which exerts chiral induction intermolecularly, then the hydrogenation stereoselectivity will be controlled both by the substrate (substrate-controlled) and by the chiral catalyst (catalyst-controlled). On occasion, this will amplify the stereoselectivity, or suppress the selectivity, and is termed double stereo-differentiation or double asymmetric induction [68]. If the directions of substrate-control and catalyst-control are the same this is a matched pair, but if the directions of the two types of control are opposite then it is a mismatched pair. 

In the above asymmetric aldol reaction, the introduction and the removal of the chiral auxiliary are carried out by simple procedures, and high asymmetric induction is achieved even at ice—bath temperature. However, at least a stoichiometric amount of a chiral auxiliary is required in such a stereo-differentiating reaction (chiral auxiliary is attached to the reactant.). 

Mosandl A, Schubert V, Stereoisomeric flavour compounds XXXIX Chiral constituents of essential oils (I), stereo differentiation of linalyl acetate — A new possibility for quality evaluation of lavender oil, Z Lebensm Unters Frosch 190 506-510, 1990. 

Bayer M, Mosandl A, Improved gas chromatographic stereo differentiation of chiral main constituents from different essential oils using a mixture of chiral stationary phases, Flavour Fragr J 19 515—517, 2004. 

Y. Izumi, A. Tai, Stereo-differentiating Reactions, Academic, New York 1977. 

During the development of MRNi, in 1977 (61a, 61b) we proposed an hypothesis about the mechanism of hydrogenation on the surface of metal catalysts (61a, 61b). In 1971-1974 we proposed the name stereo-differentiation, which is the basic principle for the so-called asymmetric reactions (24, 32, 34, 38, 62, 63). These have been the working hypotheses for the development of MRNi. 

Enantioface-differentiating ability is the most widely studied character of MRNi because MRNi has been studied with the goals of establishing the fundamental concept of stereo-differentiation and developing enantioface-differentiating catalysts for practical use. The EDA is the important parameter indicating the ability of MRNi for the production of optically active... 

The classification of stereo-differentiation (63) (see Section VII) is as follows enantiomer-differentiation includes enantioface-difTerentiation, enantiotopos-dilferentiation, and enantiomer-differentiation diastereo-differentiation includes diastereoface-differentiation, diaster-eotopos-differentiation, and diastereomer-differentiation. 

Stereo-Differentiating Hydrogenation of (R)-4-Hydroxy-2-pentanone (6) to 2,4-Pentandiol (7) with TA-NaBr-MRNi"... 

Based on the above findings, a new concept and a new term, namely stereo-differentiation (62, 63) is proposed. This concept consists of the... 

The study of silk Pd began when Dr. S. Akabori led our research group. The establishment of the experimental rule with MRNi was achieved through the contributions of Mr. M. lmaida. Dr. S. Tatsumi, Dr. T. Tanabe, Dr. T. Ninomiya, and Dr. K. Okubo. The new concept of stereo-differentiation was rationalized by the efforts of Drs. A. Tai and H. Ozaki. The development of TA-NaBr-MRNi mostly depended on the efforts of Dr. T. Harada. 

T. Hayashi and M. Kumada, Asymmetric Coupling Reactions, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 5, Chap. 5, Academic Press, New York, 1985 J. C. Fiaud, Mechanisms in Stereo-Differentiating Metal-Catalyzed Reactions. Enantioselective Palladium-Catalyzed Allylation, in A. F. Noels, M. Graziani, and A. J. Hubert, eds., Metal Promoted Selectivity in Organic Synthesis, p. 107, Kluwer Academic, Dordrecht, 1991. 

Asymmetric induction is reported in the addition of enolates of methyl ketones to aldehydes.55 Double stereo-differentiation—in which simultaneous 1,3-control can be obtained hi the aldehyde moiety—is shown to be achievable with proper selection of the aldol type. 

The above examples have presented a better induction effect when the chiral auxiliary was located at the enone molecule. Double auxiliary induction has been examined by Scharf and coworkers99. Systematic study on the photoaddition of chiral enones 203 to chiral ketene acetals 204 provides examples of matched (45% de) and mismatched (9% de) double stereo differentiation (Scheme 44). 

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