Divergent chiral compounds

In order to expand the CE potential for quantification, the selected ion monitoring (SIM) mode is to be preferred for its high selectivity and sensitivity. It can be noted that sensitivity improvement over UV-VIS spectrometry is closely related to the nature of the compound (molar absorptivity or protonation or deprotonation capacity) the awaited gain in sensitivity can diverge from about 10 to IO". Tandem mass spectrometry (MS ) appears to be relevantly advantageous for quantitative purposes [23, 37]. In fact, the selectivity issue is of crucial importance in chiral CE due to the complex composition ofthe BGE. 

Bromoenals and 1,3-dicarbonyl compounds undergo a controlled and divergent NHC (28)-catalyzed oxidative transformation treatment with an external oxidant provides 2ff-pyran-2-ones, while in the absence of an external oxidant, chiral 3,4-dihydro-2ff-pyran-2-ones are obtained in moderate to good yields and with good enantioselectivity (Scheme 46)... 

While enantioconvergent as well as divergent sequences at any rate need chiral starting materials, the very useful and highly efficient differentiation of enantiotopic groups asks only for prochiral compounds, as for instance 325. To arrive at pure enantiomers, one of the two structurally identical side chains of the starting material 325 has to be attacked enantioselectively, as is demonstrated with the Sharpless oxidation, which in this case leads to epoxide 326 as the main reaction product [115]. 

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