[reaction: see text] A new [3 + 3] Schiff base macrocycle incorporating naphthalene groups has been prepared. By examination of its properties, X-ray crystallography of model compounds, and calculations, it has been determined that the macrocycle exists predominantly as the keto-enamine tautomer. This unexpected tautomerization presents an unusual hexaketo interior in the macrocycle.

Multi-membered N-heterocycles R 0690 Tautomerization in Naphthalenediimines: A Keto-Enamine Schiff Base Macrocycle. -A model [3 + 3] Schiff base macrocycle is prepared and shown to exist predominantly as a keto-enamine tautomer (I). -(GALLANT, A. J.; YUN, M.; SAUER, M.; YEUNG, C. S.; MACLACHLAN*, M. J.; Org. Lett. 7 (2005) 22, 4827-4830; Dep. Chem., Univ. British Columbia, Vancouver, B. C. V6T 1Z1, Can.; Eng.) -R. Steudel 09-177