Kinetics and Mechanism of Addition of Benzylamines to Methyl α-Cyanocinnamates in Acetonitrile

摘要

Studies of substituent effects on the reactions of amine nucleophiles with olefins which are activated by electron-acceptors, Z and Z' in eq 1, have shown important differencein the mechanism between the reactions in aqueous solution and in acetonitrile. In aqueous solution, the reactions were found to proceed through a zwitterionic intermediate, T~±, with unbalanced transition states (TSs) in which the development of resonance into the ZZ' group lags behind charge transfer or bond formation. The lag in resonance development has been expressed by a larger α_(nuc), obtained by varying substituent Y (eq 1), thanβ_(nuc), a Bronsted type coefficient based on variation of amine nucleophile.1 The imbalance, I_m =α_(nuc) ~ β_(nuc), wasfound to increase with increasing resonance stabilization of the carbanionic product, 2, in aqueous solution, e.g., in the order CN, CN < H, NO2.