Article Dans Une Revue Tetrahedron Année : 2005

Conformational analysis of new 14-membered ring diketal dilactam macrocycles: molecular mechanics, liquid and solid state NMR studies

Résumé

A conformational study of new diversely substituted 14-membered diketal dilactam macrocycles was conducted by NMR spectroscopy in liquid and solid states, molecular mechanics calculations and, for one compound, a previous X-ray analysis. The results obtained by the different techniques show that the conformations depend closely on whether the molecules are chiral or achiral and on the stereochemistry of the ketal OMe groups. In achiral compounds, the most stable conformation of each compound has, in both the liquid and solid states, the two NH–CO links positioned perpendicular to the macrocycle plane, lending to the trans-7,7′–OMe macrocycles 6b and 7b a rectangular [3434]-type structure. In contrast, in chiral compounds, the most stable conformations are not the same in the liquid and solid phases. In the liquid state the conformations are set by the presence of one or two N4–HO1′, N4′–HO1 intramolecular hydrogen bonds that position the amide group parallel to the macrocycle plane, whereas in the solid state the amide moieties again adopt a perpendicular position which can be stabilized, when the 3-R substituent is not too bulky, by intermolecular N–HOC bonds between parallel sheets, and exceptionally, in the cis-7,7′-OMe-3,3′-Ph compound 1c, by a π–π stacking effect between the phenyl groups

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hal-00125729 , version 1 (05-03-2007)

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Denise Dugat, Ag Valade, Bruno Combourieu, J. Guyot. Conformational analysis of new 14-membered ring diketal dilactam macrocycles: molecular mechanics, liquid and solid state NMR studies. Tetrahedron, 2005, 61, pp.5641-5653. ⟨10.1016/j.tet.2005.03.073⟩. ⟨hal-00125729⟩
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