Synthesis Of 1,3,4-Oxadiazole,2-amino Oxazole Derivatives And Their Transition Metal Complexes

1,3,4-oxadiazoles and 2-amino oxazoles are heterocyclic molecules with a wide rangeof biological activity.It is very important to explore a simple method to synthesize the1,3,4-oxadiazoles and 2-amino oxazole derivatives and their metal complexes.The research contents of this paper are as follows:The 2,6-bis?5-methyl-1,3,4-oxadiazol-2-yl?pyridine?L1?and its transition metal complexes Fe?L1?2,Co?L1?2 and Ni?L1?2 have been synthesized and characterized by1 H NMR,13 C NMR,IR,single-crystal X-ray diffraction and fluorescent detection.The pyridine-2,6-dicarbohydrazide is obtained by the hydrazinolysis of pyridine-2,6-dicarboxylic acid.A ring closing reaction of pyridine-2,6-dicarbohydrazide with1,1,1-trimethoxyethane under microwave irradiation can provide 2,6-bis?5-methyl-1,3,4-oxadiazol-2-yl?pyridine?L1?.Its transition metal complexes Fe?L1?2,Co?L1?2 and Ni?L1?2have been synthesized by the reactions of the ligand L1 with Fe?BF4?2,Co?BF4?2 and Ni?BF4?2.The single-crystal X-ray diffraction showed that the single crystal of ligand L1 is monoclinic P21 / c space group and formed by the intermolecular hydrogen bond and ?-?interactions.The fluorescent test showed that Fe II can weaken the fluorescence intensity of the ligand.The magnetic data showed that Fe?L1?2 represents the antiferromagnetic properties.We provide an improved method for the synthesis of 1,3,4-oxadiazol by using DES?deep-eutectic solvents?.The DES can be used repeatedly and the operation is simple.The product of the reaction of picolinohydrazide and triethoxymethane in DES is2-?pyridin-2-yl?-1,3,4-oxadiazole.The ethyl 2-??6-fluoropyridin-2-yl?amino?-4-methyloxazole-5-carboxylate and its transition metal complexes have been synthesized and characterized by 1H NMR,13 C NMR,IR,single-crystal X-ray diffraction and fluorescent detection.The ethyl 2-amino-4-methyloxazole-5-carboxylate was synthesized by the reaction of urea and ethylacetoacetate in DES.The target compound was obtained by the substitution reaction of ethyl 2-amino-4-methyloxazole-5-carboxylate and 2,6-difluoropyridine.Its transition metal complexes CuL3Cl₂,CoL3Cl₂ and NiL3Cl₂ have been synthesized by the reactions of theligand L3 with Cu Cl₂,Co Cl₂ and Ni Cl₂.The fluorescent test showed that CuIIcan enhance the fluorescence intensity of the ligand.The complex CuL3Cl₂ represents the antiferromagnetic properties.