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.