Kinetics and mechanism of benzylamine additions to ethyl alpha-acetyl-beta-phenylacrylates in acetonitrile

Kinetic studies of the addition of benzylamines to a noncyclic dicarbonyl group activated olefin, ethyl alpha-acetyl-beta-phenylacrylate (EAP), in acetonitrile at 25.0 degrees C are reported. The rates are lower than those for the cyclic dicarbonyl group activated olefins. The addition occurs in a single step with concurrent formation of the Calpha-N and Cbeta-H bonds through a four-center hydrogen bonded transition state.The kinetic isotope effects (kH/kD > 1.0) measured with deuterated benzylamines (XC6H4CH2ND2) increase with a stronger electron acceptor substituent (deltasigmaX > 0) which is the same trend as those found for other dicarbonyl group activated series (1-4), but is in contrast to those for other (noncarbonyl) group activated series (5-9). For the dicarbonyl series, the reactivity-selectivity principle (RSP) holds, but for others the anti-RSP applies. These are interpreted to indicate an insignificant imbalance for the former, but substantial lag in the resonance delocalization in the transition state for the latter series.