Figure 4. Mechanistic and computational studies.

a, ¹H nuclear magnetic resonance (NMR) studies show that both acrylate consumption and product formation are faster in the presence of CO₂. b, Two hypotheses for the role of CO₂ in the reaction. In hypothesis 1, where CO₂ is merely a protecting group, acrylate consumption and product formation should be slower in the presence of CO₂ due to the lower concentration of free amine 9. In hypothesis 2, where CO₂ is an activator, acrylate consumption and product formation should be faster in the presence of CO₂ due to the conversion of free amine into more reactive alkylammonium carbamate 12. c, Computed thermodynamic descriptors are unable to explain rate-acceleration by CO₂ as well as high α-C−H selectivity. d, Selectivity and reactivity enhancement are achieved in the transition state (TS). e, Computed HAT transition state. f, Computational test for the role of electrostatics - removal or relocation of positive charge in the HAT reagent diminishes site-selectivity. Values are energies in kcal/mol. BDE, bond dissociation energy. B⁺ = n-C₃H₇NH₃⁺.