INFLUENCE OF THE COMPLEXATION OF COPPER(II) ON THE STRUCTURE AND REACTIVITY OF 4-HYDROXY-6-METHYL-3-[3-DIMETHYLAMINOACRYLOYL]-2H-PYRAN-2-ONE

Four novel copper(II) complexes of 4-hydroxy-6-methyl-3-[dimethylaminoacryloyl]-2H-pyran-2-one (Hacrp) have been isolated: Cu(acrp)2·1/2KCl, Cu(acrp)2(py)· H2O, Cu(acrp)(bipy)Cl·H2O and Cu(acrp)(phen)Cl·2H2O (acrp = monodeprotonated form of Hacrp; py = pyridine; bipy = 2,2′-bipyridine; phen = 1,10-phenanthroline). The crystal structures of Hacrp and Cu(acrp)2(py)·H2O have been determined. Hacrp is clearly a pyran-2-one molecule. The copper(II) ion is pentacoordinated, in a square-pyramidal stereochemistry, with py in the apical position; the acrp ligand is intermediate between the pyran-2-one form and the pyran-2,4-dione one. Both Hacrp and Cu(acrp)2(py)·H2O react with hydroxylamine hydrochloride in ethanol to give the novel molecule 8-hydroxy-5-oxo-7-methyl-5,8-dihydro-4H-pyrano[2,3-b]pyridin-4-one. Hacrp, in aqueous hydrochloric acid, transforms into 2,4-dihydroxyacetophenone. The same product has been obtained by reacting Hacrp and CuCl2·2H2O in water. Mechanisms for these reactions are proposed. © 1990.