Mechanism of Pd-catalyzed selective C-H activation of aliphatic amines via four-membered-ring cyclometallation pathway

A theoretical study is carried out on Gaunt's palladium-catalyzed selective C(sp(3))-H activation of unprotected aliphatic amines. In this reaction, the methyl group is proposed to be activated through a four-membered cyclometallation pathway even though an ethyl group is present in the substrate. Our calculation shows that the methyl and ethyl activation processes proceed in nitrogen-atom-directed pathway rather than carbonyl-directed one. More important, methyl activation is more favorable than ethyl activation with nitrogen atom as the directing group. Further studies on the structural parameters show that the lactone structure in cyclic substrate is the origin of the selective methyl activation. When the lactone moiety is changed to ketone, ether or alkyl, the selectivity could be reversed so that the ethyl activation becomes more favorable. This result validates the proposal that lactone structure is key to selective methyl activation.