title: Squaric acid N-hydroxylamides: synthesis, structure, and properties of vinylogous hydroxamic acid analogues.
abstract: The synthesis of squaric acid N-hydroxylamide esters 5 and amides 6 from dimethyl squarate 2a is described. These derivatives are analogues of the naturally occurring iron(III) chelator hydroxamic acid. On the basis of a comparative reactivity study, a concerted retro-Cope mechanism for the formation of the N-hydroxylamide esters 5 by reaction of dimethyl squarate with hydroxylamines is proposed. A preliminary iron(III) binding study of these hydroxamic acid analogues is presented, demonstrating binding of iron(III) to amides 6 in aqueous solutions, while the esters 5 did not show any sign of metal ion binding. 13C NMR spectroscopic data (chemical shift and spin-lattice relaxation time determination) of these and related derivatives delineate the resonance structures predominant in these molecules. The resonance structures of the derivatives rationalize their spectroscopic data, chemical reactivity, and iron(III) binding properties. Single-crystal X-ray structure analyses of squaric acid N-hydroxylamide ester 5b and squaric acid N-hydroxylamide amide 6c confirm their connectivity and provide structural evidence supporting the spectroscopically derived conclusions. The squaric acid N-hydroxylamides are potentially useful in the construction of chemosensors for iron(III).
authors: Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, USA.
authors: Nathaniel C
authors: NC
authors: Lim
authors: Martha D
authors: MD
authors: Morton
authors: Hilary A
authors: HA
authors: Jenkins
authors: Christian
authors: C
authors: Brückner
mesh_terms: D001667:Binding, Competitive; D018360:Crystallography, X-Ray; D003503:Cyclobutanes / Q000138:chemical synthesis* / Q000737:chemistry; D005290:Ferric Compounds / Q000032:analysis / Q000737:chemistry; D006877:Hydroxamic Acids / Q000138:chemical synthesis* / Q000737:chemistry; D006898:Hydroxylamines / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D013329:Structure-Activity Relationship; D014753:Vinyl Compounds / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D003503:Cyclobutanes; D005290:Ferric Compounds; D006877:Hydroxamic Acids; D006898:Hydroxylamines; D014753:Vinyl Compounds; C030042:squaric acid