Small Organic Molecules Chemically Selective Catalytic Asymmetric Reactions And Theoretical Research Stereoselectivity

Bifunctional organocatalysts have been developed in the direct asymmetric reactions in recent years. Lots efforts have been devoted on the design of new catalysts and the catalytic activities. However, the origins of the mechanism and stereoselectivity still remain elusive, which hinder the development of new catalysts and wide application of asymmetric reactions. Mechanical investigations have been studied in the asymmetric aldol and Mannich reactions with the density functional theory. The essence of asymmetric catalysis has been explored and it could be helpful for the design of new catalysts.First, the detailed mechanism of proline and axially chiral amino sulfonamide-catalyzed cross-aldol reactions between different aliphatic aldehydes have been explored with the density functional theory. The calculations for the enamine formation and the crucial C-C bond-formation reveal the origins of the chemoselectivies and stereoselectivies.Second, the calculations have been performed in proline and amino sulfonamide-promoted aldol and Mannich reactions involving special electrophiles using the BHandHLYP method. The results reproduced the different stereoselectivities of the two chiral secondary amino catalysts-promoted asymmetric reactions.Finally, the detailed calculations in the isoleucine-catalyzed cross-aldol reactions between enolizable aldehydes have been studied with density functional theory in chapter five. First, the investigations for enamine formation have been explored and compared with the proline promoted processes, which provide rational explanations for chemoselectivies of primary and secondary amino acid-catalyzed processes. Then computations demonstrate the rationalization of different stereoselectivies for stereo-controlling steps in contrast to conventional aldol reactions.