Chirality chemical

Chiral chemical reagents can react with prochiral centers in achiral substances to give partially or completely enantiomerically pure product. An example of such processes is the preparation of enantiomerically enriched sulfoxides from achiral sulfides with the use of chiral oxidant. The reagent must preferential react with one of the two prochiral faces of the sulfide, that is, the enantiotopic electron pairs. 

Available from Daicel Chemical Industries, Ltd. Chiral Chemicals Division, 2-5, Kasumigaseki 3-chome, Chiyoda-ku 100-607 7, Tokyo, Japan. 

Preferential screw sense helix induced by chiral side groups and/or chiral chemical influence... 

Most chiral chemicals are relatively small-scale products (1 to 1000 tonnes per year for pharmaceuticals, 500 to 10000 tonnes per year for agrochemicals) that are usually produced in multipurpose batch equipment This is probably the case for most catalytic reactions described in this chapter however, as a rule very little information on process technology is provided by the manufacturers. Here, we will discuss only briefly the reactor choices for hydrogenation reaction typically carried out in the liquid phase. For a successful implementation the following demands must be met ... 

Chiral chemical shift reagents for NMR analysis are also useful, and so are optical methods. 

Achiral lanthanide shifting reagents may be used to enhance the anisochrony of diastereomeric mixtures to facilitate their quantitative analysis. Chiral lanthanide shift reagents are much more commonly used to quantitatively analyze enantiomer compositions. Sometimes it may be necessary to chemically convert the enantiomer mixtures to their derivatives in order to get reasonable peak separation with chiral chemical shift reagents. 

Scheme 1-3. Determining enantiomer composition with chiral chemical shift reagent 18.

Handbook of Chiral Chemicals, ed. D. J. Ager, Marcel Dekker, New York, 1999. 

A particular case is "absolute asymmetric induction" which requires a chiral physical force-such as circularly polarised light- rather than a chiral chemical reagent. 

Shi Y (2006) In Ager D (ed) Handbook of chiral chemicals, 2nd edn. CRC, Taylor Francis Group, Boca Raton, Chap. 10... 

There is currently great interest in the flavor and fragrance industry in developing natural chiral chemicals from plant materials. The interest in natural chiral chemicals continues to grow for several reasons ... 

Ager, D. (ed.) (2006) Handbook of Chiral Chemicals, 2nd edn, CRC Press/Taylor Frands, Boca Raton, FL. 

H.U. Blaser, M. Lotz, F. Spindler, "Asymmetric Catalytic Hydrogenation Reactions with Ferrocene Based Diphosphine Ligands" in Handbook of Chiral Chemicals, 2nd Edition, D. J. Ager (Ed.), CRC Press, Boca Raton 2005... 

The Julia - Colonna asymmetric epoxidation of electron-deficient unsaturated ketones to the corresponding epoxides with high yields and high ee is well known. This technique produces chiral chemical entities from the clean oxidant, hydrogen peroxide, without the use of a toxic or water sensitive transition metal additive. 

Retention of Heterogenized Chiral Chemical Catalysts in a Membrane Reactor... 

While enzymes and chiral chemical catalysts compete for best performance in a variety of situations, they have also been used jointly to afford a desired reaction result (Choi, 1999). By far the most frequent application of this concept, termed an enzyme-metal combi reaction (EMCR) , is the dynamic kinetic resolution (DFR) of a racemic mixture with a lipase and an organometallic complex to afford in-situ racemization. 

In modern stereochemistry asymmetric reactions1-24 play an increasing role in the solution of problems involving chiral chemical compounds and in their preparation. Asymmetric reactions are useful in elucidating the structural features of chiral molecules and in the study of reaction mechanisms, including those of biochemical reactions. Their importance is further emphasized by the realization that all naturally occurring chiral chemical compounds stem from asymmetric syntheses. 

Predictably, there will be an increasing tendency to prepare chiral chemical compounds by asymmetric syntheses as the understanding of their methodology grows. 

The cooperativity of amplification, switching, and memory in synthetic helical polymers might thus be shared with ideas of a scenario for the biomolec-ular homochirality, autocatalytic mechanism in chiral chemical synthesis, and bifurcation equilibrium mechanisms in crystallization of chiral crystals. Indeed, amplification phenomena in several optical activity and helicity of synthetic polymers in isotropic solution appears to be common and are now established as sergeants and soldiers experiment and majority rules in polymer stereochemistry [17,18]. Any minute chiral forces caused by intramolecular and intermolecular systems can be detectable, when a proper model polymer system is chosen to elucidate the cooperativity of amplification, switching, and memory. 

M. Avalos et al., From parity to chirality Chemical implications revisited. Tetrahedron Asymm. 11, 2845-2874 (2000)... 

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