Chiral compounds formed during

By using high resolution capillary gas chromatography, the scope of use of these reagents, which were initially introduced for NMR-analysis (5J and for GC separation of secondary alcohols (6), was enlarged considerably (7,j3). The application of these methods to the analysis of optically active compounds formed during microbiological processes and to the determination of the enantiomeric composition of chiral aroma constituents in some tropical fruits is described in this paper. 

In summary, the SMS reaction is a truly efficient process, possessing a broad scope and applicable to a number of carbonyls, allylsilanes, alcohols (silyl ethers) or amines. Its usefulness has been validated in several total syntheses and demonstrated by the preparation of chiral homoallylic alcohols. During the development of the SMS reaction, Melkafia and Marko [48] realized that the homoallylic alcohol (ether), if connected to an allylsilane, would form novel annelating agents that would lead to tetrahydropyran derivatives via condensation with carbonyl compounds. This reaction was called IMSC for intramolecular Sakurai cydization and will be discussed in the next section. 

Another example of intramolecular CT complex formation is provided by trans-4-dimethvlamino-4 -(1-oxobutvl)stilbene Solvent effects on the spectrum give a value of 22D for the excited state dipole moment. The effect of electric field on the fluorescence of 4-(9-anthry1)-N.N.-2.3,5,G-hexamethy1-aniline shows this compound forms an excited state whose dipole moment does not change with solvent . Chiral discrimination in exciplex formation between 1-dipyrenylamine and chiral amines is very weak . In the probe molecule PRODAN (6-propionyl)-2-(dimethylamino)—naphthalene the initially formed excited state converts to a lower CT state as directly evidenced by time-resolved spectra in n-butanol. Rate constants for intramolecular electron transfer have been measured in both singlet and triplet states of covalently porphyrin-amide-quinone molecules . Intramolecular excimer formation occurs during the lifetime of the excited state of bis-(naphthalene)hydrazides which are used as photochemical deactivators of metals in polyethylene . ... 

The ideal way to obtain pure drug enantiomers would be enantioselective synthesis. This, however, is rarely practical, usually complicated, and almost always expensive. There is little control over which chiral form of a chemical compound will be formed during a typical production process. This lack of control generally results in production of equal amounts of the various possible chiral forms of a compound. Often, therefore, separation of intermediates or final products from a racemic mixture is required. Increasing interest is being paid to development of methods of efficient, high throughput, and sensitive chiral separations, control of chemical synthesis, assessment... 

The most important advantages of direct chromatographic enantioseparations for preparative purposes include the presence of resolved enantiomers in original and high optically pure form in different volume fractions of the mobile phase, no loss of chiral selectors, and amost no risk of contamination of desired enantiomers with the chiral selector. Parallel to enantioseparations other impurities may be removed from chiral compounds during this process. 

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