Mechanism of the Organocatalyzed Decarboxylative Knoevenagel-Doebner Reaction. A Theoretical Study

We have investigated important intermediates and key transition states of the organocatalyzed Knoevenagel condensation using density functional theory and two different basis sets (6-31 G(d,p) and 6-311++G(2df,2pd)), both in gas phase and simulating the bulk solvent (pyridine) using the PCM method. Calculated structures for reactants, intermediates, and key transition states suggest that the secondary amine catalyst is essential, both for activating the aldehyde for nucleophilic attack, and in the possible decarboxylation pathways. The calculated results are shown to agree with available experimental information. On the basis of the results obtained, the studied mechanism may be important in the understanding of vinylphenol production during malting and brewing of wheat and barley grains.