Kinetic and Mechanistic Investigation of Asymmetric Organocatalytic Reactions

Abstract

The utilisation of the reaction progress kinetic methodology to advance the mechanistic understanding of the asymmetric proline catalysed aldol and α-aminoxylation reactions is demonstrated in this work. Mechanistically meaningful reaction rate laws that describe the catalytic cycles of these reactions are derived experimentally, using initially the power law driving force analysis. With the aid of the employed kinetic methodology it is shown that the processes occurring on the catalytic cycle can be deconvoluted from the influence of the reactions occurring off the cycle, and each may be studied separately. It is also shown that the synergetic efforts of experimental kinetic and spectroscopic studies are capable of suggesting and ultimately disclosing the role of additives in these reactions and understanding of catalyst deactivation pathways. In order to obtain more support towards the kinetically derived mechanistic implications, kinetic isotope studies of the aldol reaction were performed. Experimental kinetic data fit to the derived rate model helped to assess and refine the proposed mechanism of the aldol reaction in a quantitative manner and consider other factors that potentially may affect the reaction. The rationalisation of the difference in kinetic behaviour of the aldol and a- aminoxylation reactions is discussed. The proposed elucidation is also supported by reaction simulations performed using COPASI simulation software