Synthesis,Spectroscopy And Structural Analysis Of Cyclic ?-Diketimine Compounds

Compared with ?-diketimine compounds,which are widely used in coordination chemistry,there are only scarce reports on the synthesis and utilizations of their cyclic counterparts.The coordination chemistry of cyclic ?-diketimine compounds are even unexplored.In this work,a series of cyclic ?-diketimine compounds have been synthesized.Specificically,the condensation of 2,6-disubstituted anilines and cyclic?-diketone has been achieved,to provide the corresponding cyclic?-diketimine.compounds.Their structures have been authenticated by spectroscopic techniques.Nine cyclic ?-diketimine compounds were synthesized by the condensation reactions between cyclic ?-diketone and 2,6-unsubstituted,2-monosubstituted anilines or ?-naphthylamine in a molar ratio of 1:2,in the presence of one equivalent of p-toluenesulfonic acid,refluxing.in toluene for.12-36 h.Nevertheless,when the aromatic amines are 2,6-disubstituted anilines.(2,6-dichloroaniline,2,4,6-trimethylaniline,2,6-dimethylaniline,2,6-diisopropylaniline),only the monocondensed enaminones were obtained under the same conditions.The enaminones didn't condense with 2,6-disubstituted anilines using literature methods,such as refluxing in toluene catalyzed p-toluenesulfonic acid,refluxing in HCl/ethanol or via oxonium intermediates formed by treating enaminones with ethyl iodide or boron tetrafluoride ethoxium salt.Finally,the double condensation of cyclic ?-diketone and 2,6-disubstituted anilines in 1:2 molar ratio was achieved by refluxing in high boiling point solvent mesitylene(b.p.:163-166?)over a period of 120 h,in the presense of one equivalent p-toluenesulfonic acid with yields between 50-70%.The reaction time was shortened to 60 h when two equivalents of p-toluenesulfonic acid were employed.Cyclic ?-diketimines can alternatively be prepared by refluxing enaminones,anilines and p-toluenesulfonic acid in a 1:1:1 molar ratio in mesitylene for about 50-60 h,and the sterically hindered unsymmetric cyclic ?-diketimines could thus be prepared.All intermediates and cyclic ?-diketimines were fully characterized by 1H NMR,13C NMR,MS,IR,and UV-Vis spectroscopies.The molecular structures of one cyclic enaminone and four cyclic?-diketimine compounds were determined by X-ray single crystal diffraction analysis.In the solid state,they display one-dimensional supermolecular motifs chained by hydrogen bonds.One of the structures shows that a methanol molecule is trapped in the crystal of the cyclic?-diketimines derived from 2,6-diisopropylanaline,bridging two?-diketimine molecules by hydrogen bonds due to the use of methanol in the workup.The methanol can only be completely removed by vacuuming above 95? for 3-4 h.In summary,this work has achieved the synthesis of the cyclic?-diketimines derived from 2,6-disubstituted anilines.Twelve intermediates and fifteen cyclic ?-diketimines were synthesized and nineteen of them are unreported compounds.Theforce,these compounds are ready for further investigation in coordination chemistry and materials science.