Behaviour of nitrile oxides towards nucleophiles. Part II. Substituent effect on the rate of dimerisation of aromatic nitrile oxides to 3,6-diaryl-1,4,2,5-dioxadiazines

Abstract

The dimerisation of aromatic nitrile oxides to 3,6-diaryl-1,4,2,5-dioxadiazines catalysed by suitable nucleophiles is shown to follow either second- or third-order kinetics, according to the substituents. An increase in the base strength of the nucleophile causes a change in reaction order from three to two and an increase in rate constant, while an increase in electron-withdrawing power of the nitrile oxide ring shows only this second effect. These results agree with a reaction scheme in which an intermediate adduct between nitrile oxide and nucleophile reacts with more nitrile oxide to give the dimer.