Thermal elimination reactions of nitrones. Part 2. A mechanistic study based on substituent and solvent effects

Abstract

The rates of thermal elimination of isobutene from a series of N-(diarylmethylene)-t-butylamine N-oxides have been measured by u.v. spectroscopy. Activation parameters derived for N-(fluoren-9-ylidene)-t-butylamine N-oxide in decalin and t-butyl alcohol solvents are consistent with an intramolecular concerted mechanism involving a highly ordered cyclic transition state. Kinetic results from the thermal elimination of para-substituted N-(diarylmethylene)-t-butylamine N-oxides in protic and aprotic solvents however suggest that the reaction proceeds via a non-synchronous concerted mechanism in contrast to the Cope elimination of tertiary amine oxides.