Scope and Mechanism of the Ruthenium-Catalyzed Deaminative Coupling Reaction of Enones with Amines via Regioselective Cα–Cβ Bond Cleavage

A highly regioselective C–C bond cleavage method of enones has been devised from the ruthenium-catalyzed deaminative coupling reaction with simple amines. The analogous catalytic coupling reaction of enones with anilines has led to a regioselective Cα–Cβ bond cleavage of enones in forming N-alkylanilines and 2,4-disubstituted quinolines. The reaction profile study showed the formation of a β-aminoimine intermediate prior to the C–C cleavage product formation. A Hammett plot from the reaction of (E)-2-octen-4-one with a series of para-substituted benzylamines established a strong promotional effect by an electron-donating group (ρ = −0.77 ± 0.1). The most significant carbon kinetic isotope effect was observed on the α-carbon of the product (Cα = 1.018). The DFT calculations revealed a detailed mechanism of the coupling reaction via consecutive C–H activation and C–C cleavage steps, followed by enamine-to-imine rearrangement and hydrolysis steps. The catalytic method combines hydrogen borrowing and deaminative coupling strategies to furnish a general Cα–Cβ bond cleavage protocol for enones.