Molecular and crystal structures of N,N′-propylene- and N,N′-phenylene-diylbis [3-(1-aminoethyl)-6-methyl-2H-pyran-2,4(3H)-dione]

Two macrocyclic ligands, N,N′-propylene-diylbis[3-(1-aminoethyl)-6-methyl-2H-pyran-2,4(3H)-dione] I and N,N′-phenylene-diylbis[3-(1-aminoethyl)-6-methyl-2H-pyran-2,4(3H)-dione] II, have been prepared by the condensation of dehydroacetic acid (3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one) with 1,2-phenylenediamine and 1,3-propylenediamine. They have been characterized by means of elemental analysis, IR spectroscopy as well as by X-ray crystallography. The molecular structures of the compounds I and II can be described as consisting of two β-enaminone-2-pyrone rings interlaced with either alkyl chain in I or phenyl ring in II. The X-ray studies confirmed the existence of strong N-H⋯O intramolecular hydrogen bonds in both structures. Their lengths are in accordance to lengths of RAHB intramolecular hydrogen bonds in 1,3-diketones, aryl-hydrazones, β-enaminones and related heterodienes (2.5-2.6 Å) [P. Gilli, V. Bertolasi, V. Ferretti and G. Gilli, J. Am. Chem. Soc., 122 (2000) 10405].