Mild and selective reduction of imines: formation of an unsymmetrical macrocycle.

During investigations of 5, a [3 + 3] Schiff-base macrocycle with six imines, a partially reduced Schiff-base macrocycle, 6, possessing one CH(2)NH and five imine groups was obtained. Control experiments and deuterium labeling indicate that the macrocycle is reduced by a benzimidazoline generated during the reaction. Benzimidazolines may be convenient reagents for the mild and selective reduction of imines.