Effect Of The Tether Length Upon Truce-Smiles Rearrangement Reactions

This report examines the effect of substrate design upon the Truce-Smiles rearrangement, an intramolecular nucleophilic aromatic substitution reaction. The length of the molecular spacer that tethers the carbanion nucleophile to the substituted benzene ring was found to have a strong influence on the ability of the substrate to undergo the reaction successfully. Our experimental results show highest yield of desired aryl migration product for substrates designed with a 3-atom tether, which proceed through a 5-membered spirocyclic intermediate. The results are interpreted in comparison with a survey of Truce-Smiles rearrangements described in the literature and found to be consistent. Computational studies support the observed reactivity trend and suggest an explanation of a favorable combination of ring strain and electrostatic repulsion leading to optimal reactivity of the substrate designed with a 3-atom tether. Comparison of our results with trends for related ring-closing reactions illustrate the unique electrostatic features of the system studied herein.