Molecular catalysis by quaternary ammonium salts: cyclisation of 2-(3-halopropyl)-4-nitrophenols

The cyclisation of 2-(3-halopropyl)-4-nitrophenols 4-6 is an intramolecular nucleophilic substitution with clean first-order kinetics. The rate is influenced by the macrotricyclic ammonium salt 2 by virtue of a 1:1 hostguest complex formation. Inhibition is observed with the chloro compound 4 and to a minor extent with the bromo analog 5, whereas a moderate rate acceleration was found with iodo compound 6. Inspection of the temperature dependence of the rate effects leads to the conclusion that 2 may be regarded as a dipolar aprotic microsolvent.