Reactions of N-Chlorobenzylmethylamines with Secondary Amines in Acetonitrile. Effect of Base Strength upon the Imine-Forming Transition State

Reactions of N-chlorobenzylmethylamines 1 with R₂NH in MeCN have been investigated kinetically. Eliminations from 1 were quantitative and regiospecific, producing only benzylidenemethylamines. For the elimination reaction of 1 with Bu₂NH, k_H/k_D = 8.8, p = 0.96, ΔH* = 7.6 kcal/mol, and ΔS^#= -45.1 eu were determined. The transition state structure is assessed as being highly symmetrical with similar extents of C_β-H and Nα-C1 bond cleavage, little carbanionic character, and significant π bond formation. The k_H/k_D and p values first increase and then decrease with enhancing amine base strength. Comparison of these results with those for related olefin-forming eliminations provides insight into the transition state differences between imine- and olefin-forming eliminations.