Kinetics and Mechanism of the Addition of Benzylamines to Benzylidenediethylmalonates in Acetonitrile

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Abstract
Kinetic studies of the benzylamine additions to benzylidenediethylmalonates (BDM: YC6H4CHC(COOEt)2) in acetonitrile at 20.0 °C are reported. The rates in acetonitrile are consistent with that expected from the through-conjugative electron-accepting power of the activating groups, (COOEt)2. The sign and magnitude of the cross-interaction constant, ρXY = −0.45, are in general agreement with those for the single-step amine additions to activated olefins. The kinetic isotope effects (kH/kD > 1.0) measured with deuterated benzylamines (XC6H4CH2ND2) increase with a stronger electron-acceptor substituent in benzylamines (∂σX > 0) and a stronger electron donor in the substrate (∂σY < 0). These trends are the same as those found for benzylidene-1,3-indandiones but are exactly opposite to those for other activated olefin series, e.g., β-nitrostyrene. It has been shown that the former series are thermodynamically controlled, whereas the latter are intrinsically controlled with a relatively strong transition state imbalance. The activation parameters, ΔH⧧ and ΔS⧧, also support our proposed transition state involving concurrent CαN and CβH bond formation with a four-membered cyclic structure.