Asymmetric destruction

Optically active fr ws-2,3-di-/-butylcyclopropanone has been prepared by asymmetric destruction of the racemic compound with d-amphetamine.64> The (+)-cyclopropanone, [a]ls6+76° (c 0.5, CCI4) exhibits a positive Cotton effect with a peak at 370 nm. Racemization occurs upon heating. 

Asymmetric synthesis is observed if the interest focuses on the product side of the reaction (Sec. II.C). The nonracemic products may be created by asymmetric destruction or stem from reactants kept racemic by fast ground state enantiomerization. 

In order to summarize the papers on asymmetric destruction, the format of Inoue [37], who used a table, seems to be appropriate. His listing is completed in Table 1. 

Table 1 Direct Asymmetric Destruction with Circularly Polarized Light in Solution81 ... 

As stated in Sec. B, asymmetric synthesis is the other side of the coin of asymmetric destruction the products are in the focus of interest. However, there are at least two types of reactions to be considered independent and dependent parallel reactions. The latter, starting from a prochiral racemic mixture of reactants, are often considered the real representatives of asymmetric synthesis. 

Several of the papers dealing with asymmetric destruction also report information about the enantiomeric excess of the products in the sense of independent asymmetric reactions. If the data of both reactants and products can be determined independently, the degree of transfer of asymmetry may be used for mechanistic questions [10] according to Eq. (38). 

Irradiation performed with racemic substrate at room temperature, unless noted otherwise. Anisotropy (g) factor at or around irradiation wavelength, if reported or estimated. Extent of destruction. Maximum observed rotation a of irradiated solution, or specific rotation [a] of isolated sample or of residue obtained upon evaporation. Maximum observed ellipticity of irradiated solution or molar ellipticity of isolated sample. Enantiomeric excess of isolated sample. Not reported. Compound (mp 113 C) of unknown structure, obtained in a reaction of humulene with sodium nitrite, according to the reported procedure Chapman, AC. J. Chem. Soc. 1895 67 780. A mixed case of asymmetric destruction and photoderacemization irradiation performed at 0 C. Enantiomerically enriched sample used. Estimated g factor enhanced by two-quantum excitation with high intensity picosecond laser pulse. High-inten-sity laser of indicated pulse duration used. "Irradiation performed at 77 K in a hydrocarbon glass matrix. Optically pure sample photolyzed only to evaluate the enhanced g factor. Estimated g factor enhanced by two—quantum excitation with high-intensity femtosecond laser pulse. 

It seems worthwhile to consider whether chiral induction during the conrotatory cyclization process, asymmetric destruction of one of the enantiomers, or a more complex process is involved in this reaction. Further study would be required to resolve this question. 

The multitude of terms in the literature, describing the outcome of a given chemical transformation, is a result of the need to emphasize a particular characteristic or selective aspect of a given transformation, e.g. stereoselectivity of the process, optical purity of the product(s), the generation or destruction of an asymmetric center during the transformation, etc.. Asymmetric synthesis, chiral synthesis, asymmetric induction, asymmetric destruction, kinetic resolution, asymmetric desymmetrization are such terms - ones that have described well, specific aspects of a wide variety of reactions. To date, there has been no attempt to depict all of these aspects as parts of a "big picture." Indeed, the problem of a systematic universal classification of chemical transformations has remained unsolved. 

With increasing stereochemical complexity of novel synthetic transformations, terms such as asymmetric transformation, asymmetric synthesis, asymmetric destruction, asymmetric induction, kinetic resolution have been developed chronologically, as dictated by the need for... 

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