REACTIONS OF N-(ARYLSULFONOXY)-N-ALKYLBENZYLAMINES WITH MEONA-MEOH - STERIC EFFECT ON THE STRUCTURE OF THE IMINE-FORMING TRANSITION-STATE

Elimination reactions of N-(arylsulfonoxy)-N-alkylbenzylamines 1-5 with MeONa-MeOH have been studied kinetically. The elimination reactions are regiospecific, producing only corresponding benzylidenalkylamines. The rate equation for the reactions is k(obs) = k0 + k2[MeONa], indicating that the reactions proceed by competing solvolytic- and base-promoted pathways. The relative rates of elimination for the k2 and k0 pathways are 1, 0.67, 0.53, 0.35, and 0.27 for R = Me, Et, i-Pr, s-Bu, and t-Bu and 1, 4.1, 5.1, and 8.7 for R = Et, i-Pr, s-Bu, and t-Bu, respectively. For MeONa-promoted elimination from 1-5, Hammett-rho and k(H)/k(D) decrease but rho-1g and \beta-1g\ increase with a bulkier alkyl substituent. However, the values for the solvolytic eliminations are nearly the same for all substrates and are similar to those for the base-promoted pathway, except for the rho-values, which have opposite signs. From these results, the changes in transition-state structure wrought by variation of N-alkyl substituents are assessed.