Mechanism and Origins of Regioselectivity of Selenium-Catalyzed Allylic Amination Reactions

The mechanism of the selenium-catalyzed allylic amination reactions with different ligands has been explored with density functional theory calculations. The mechanism consists of the generation of the key active catalyst selenium bis(imide), ene reaction, [2,3]-sigmatropic shift, and ligand-assisted hydrogen transfer. The ene reaction step plays a critical role in determining the regioselectivity of the reaction. Under two different catalytic conditions (Cy₃PSe and IMeSe), OPCy₃ and OIMe were identified as the most optimal ligands. The computational results indicate that the ene reaction does not occur through a simultaneous ligand dissociation process, but rather proceeds in a stepwise manner where the ligand dissociates before engaging in the ene reaction with the substrate. Furthermore, the regioselectivity mainly originates from the orbital interaction for acyclic trisubstituted alkenes and the distortion energy for cyclic trisubstituted alkenes.