Theoretical Study on the Mechanism of the Petasis‐type Boronic Mannich Reaction of Organoboronic Acids, Amines, and α‐Hydroxy Aldehydes

The mechanism of a typical Petasis‐type boronic mannich reaction (the styrylboronic acid, dibenzylamine, and α ‐hydroxylpropionaldehyde) has been investigated using density functional theory calculations. According to our calculations, the reaction is most likely to proceed through the following steps: 1) the nucleophilic addition of the amine to the aldehyde to form the carbinolamine; 2) the dehydration of the carbinolamine; 3) the formation of the tetra‐coordinated borate intermediate; 4) the CC bond formation by the intramolecular transfer of the styryl group; 5) the hydrolysis of the resulting intermediate to give the final products. The highest point on the energy profile is the transition state for the CC bond formation (118.8 kJ·mol −1 above the reactants in ethanol). Our results can give reasonable explanations on some experimental facts observed for many Petasis‐type boronic Mannich reactions.