Nucleophilic Substitution Reactions of Thiopheneethyl Arenesulfonafes with Anilines and N,N-Dimethylanilines

Nucleophilic substitution reactions of 2-thiopheneethyl benzenesulfonates (2-TEB) and 3-thiopheneethyl benzenesulfonates (3-TEB) with anilines and N,N-dimethylanilines (DMA) are investigated in acetonitrile at 60.0 C. The cross-interaction constants ρ XZ determined for the reactions with anilines are large negative (− 0.50) which are comparable to those for the similar predominantly frontside-attack S N2 reactions of 1-phenylethyl (1PEB), 2-phenylethyl (2-PEB) and cumyl benzenesulfonates. A large negative ρ XZ value (− 0.4~ − 0.8 ) is considered to provide a mechanistic criterion for the frontside-attack S N 2 mechanism with a four-center transition state. In agreement with this proposal the kinetic isotope effects, k H/ k D, involving deuterated aniline nucleophiles are all greater than one reflecting partial N-H(D) bond cleavage in the transition state. The MO theoretical reactant structures of 1-PEB, 2-PEB and 2-TEB based on the PM3 calculation show that the benzene ring blocks the backside nucleophile approach to the reaction center carbon (C α) enforcing the frontside-attack S N 2 mechanism.