Kinetics and mechanism of benzylamine additions to ethyl α-acetyl-β-phenylacrylates in acetonitrile

Abstract

Kinetic studies of the addition of benzylamines to a noncyclic dicarbonyl group activated olefin, ethyl α-acetyl-β-phenylacrylate (EAP), in acetonitrile at 25.0 °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 C_α–N and C_β–H bonds through a four-center hydrogen bonded transition state.

The kinetic isotope effects (k_H/k_D > 1.0) measured with deuterated benzylamines (XC₆H₄CH₂ND₂) increase with a stronger electron acceptor substituent (δσ_X > 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.