Deciphering competing reaction pathways in the α-C–H functionalization of unprotected alicyclic amines via ketone-mediated hydride transfer

Abstract

Alicyclic amines are pervasive in pharmaceuticals and natural products, yet direct α-C–H functionalization of unprotected secondary amines remains a long-standing challenge. Building on the historical oxidation of lithium amides by ketones, we present a combined experimental and computational study that establishes the mechanistic basis for α-functionalization of these substrates. Competition experiments, ReactIR monitoring, kinetic isotope effects, and DFT calculations demonstrate that imine formation proceeds through concerted hydride transfer from solvent-coordinated monomeric lithium amides. Nucleophilic addition of lithium amides to the ketone oxidant is identified as a major yield-limiting side reaction and is shown to depend strongly on amine ring size, oxidant electrophilicity, and steric effects. Regioselectivity in α-substituted amines arises from a combination of steric and electronic factors governing C–H bond activation. These findings clarify the fundamental reactivity of lithium amides and provide a practical platform for the synthesis of polysubstituted alicyclic amines without protecting groups or transition metals.