Revisiting the Passerini
Reaction Mechanism: Existence
of the Nitrilium, Organocatalysis of Its Formation, and Solvent Effect
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Abstract
The Passerini reaction mechanism
is revisited using high-level
DFT calculations. Contrary to the common belief, the nitrilium intermediate
is found to be stable in solution and its formation is rate-determining.
The present results point out that this step is catalyzed by a second
carboxylic acid molecule, as the subsequent Mumm rearrangement is.
The solvent effect on the reaction rate was investigated. In a protic
solvent like methanol, hydrogen bonds are responsible of the increasing
barrier of the rate-determining step, compared to the commonly used
solvent, the dichloromethane