Test synthesis, tools

For 10 years, attention has been focused on the intramolecular additions ofallylic and alkynyl-silanes to enones. In early studies, a variety of Lewis acids were tested and reaction conditions were optimized to make this reaction a powerful tool in the synthesis of spiro-annulated, and 1,2-fused ring systems, which can be utilized in the total synthesis of natural products34,35. 

The DPE reduction is used as a test reaction to characterize the materials and optimize the preparation conditions of the catalyst. Since hydroaluminations can also be used for the synthesis of carboxylic acids, deuterated products, or vinyl halides via quenching with CO2, D2O or Br2 [44], the method is also a valuable organic synthesis tool. However, as compared with molecular catalysts like Cp2TiCl2 that are known to catalyze hydroaluminations [44], the titanium nitride materials described here are solid catalysts and can be separated by centrifugation. Moreover, they can be reused several times, which is an advantage as compared to molecular catalysts. 

In gas phase reactions the size of catalyst libraries can be over couple of thousands. For instance, in the synthesis of aniline by direct amination of benzene around 25000 samples were screened in about a year [15], however, the optimization method used was not discussed. In contrast, in liquid phase reactions taking place at elevated pressure and temperature, due to technical difficulties the rational approach does not allow testing libraries containing more than 200 250 catalysts. Consequently, the informatic platform and the strategy used to design catalyst libraries for high-pressure liquid phase reactions should have very unique optimization tools. 

At least two systems can be cited as catalysts of peroxide oxidation the first are the iron (III) porphyrins (44) and the second are the Gif reagents (45,46), based on iron salt catalysis in a pyridine/acetic acid solvent with peroxide reagents and other oxidants. The author s opinion is that more than systems for stress testing these are tools useful for the synthesis of impurities, especially epoxides. From another point of view, they are often considered as potential biomimetic systems, predicting drug metabolism. Metabolites are sometimes also degradation impurities, but this is not a general rule, because enzymes and free radicals have different reactivity an example is the metabolic synthesis of arene oxides that never can be obtained by radical oxidation. 

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