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Abstract:
In the last few years organocatalysis has emerged as a new catalytic method based on metal-free organic molecules. In many cases these often small compounds give rise to extremely high enantioselectivity. Usually the reactions can be performed under an aerobic atmosphere with non-anhydrous solvents. The catalysts can be easily synthesized in both enantiomerically pure forms and are often more stable than enzymes or other bioorganic catalysts. Despite the significant growth in the number of organocatalytic researches, still the mechanistic details of many reactions are not fully understood. The knowledge of the reaction mechanism on the other hand is important to optimize the reaction conditions toward higher reaction efficiency. Structural elucidation of organic compounds is commonly achieved by analytical techniques such as NMR-, UV/Vis- or IR-spectroscopy. The information gained from these methods is essential for the characterization of the reactive intermediates and thus the reaction mechanism investigation. These spectroscopic methods however have enormous limitations when the compounds of interest are existent only in low concentrations or have very short life times.
Mass spectrometry is the method of choice for the analysis of rapid and complex catalytic reactions. Because mass spectrometry is generally a very fast and sensitive technique, it is capable of investigating compounds with short life times and in low concentrations. In addition it is also possible to characterize different analytes at the same time without separation and, with MS/MS experiments, to perform a structural elucidation of each of these directly from the reaction solution.
High resolution MS can be used to gain the elemental composition of the unknown analyte(s), which can give further insight into the studied mechanisms and the compounds that are involved.
Different mechanistic studies of complex organocatalyzed reactions are presented in this work. These reactions have been investigated using unique methods of mass spectrometry such as isotopic labeling, online monitoring and ion/molecule reactions in the collision cell of the mass spectrometer.
