REACTIONS OF (E)-O-ARYLBENZALDOXIMES WITH SECONDARY-AMINES IN ACETONITRILE - EFFECT OF BETA-ARYL SUBSTITUENTS UPON THE COMPETITION BETWEEN E2 AND SNAR REACTIONS

Reactions of (E)-O-arylbenzaldoximes in which the O-aryl group is 2,4-dinitrophenyl (1a-d) and picryl (2a-d) with secondary amines in acetonitrile have been studied kinetically. The reactions proceeded via competing E2 and S(N)Ar mechanisms. For eliminations from 1a-d promoted by R2NH in MeCN, the transition state was changed toward Elcb-like by a more electron-withdrawing beta-aryl substituent and a stronger base. On the other hand, the transition states for eliminations from 2a-d and for the S(N)Ar reactions of all substrates were relatively insensitive to the variation of either beta-aryl substituent or base strength. The yield of S(N)Ar product increased with base concentration, electron-withdrawing ability of the O-aryl group, and base strength. When the electron-withdrawing ability of the beta-aryl substituent is increased, the yield of S(N)Ar product from 1a-d decreased, although no clear trend was observed for 2a-d. From these results, factors that influence the competition between E2 and S(N)Ar reaction pathways are assessed.