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The Syntheses, Characterization and Crystal Structures of a Series of Heterocyclic β-Diketones and Their Isoxazole Compounds

Author(s):

Biyun Su*, Yifan Hou, Li Wang, Xiaoteng Li, Dandan Pan, Tingyu Yan, Ao Zhang, Faida Paison and Liqing Ding   Pages 1 - 11 ( 11 )

Abstract:


Background: In the field of coordination chemistry, the introduction of heterocyclic substituents into structure of β-diketone enables ligand to produce multiple coordination sites, the adoption of small steric oxime group into the structure of heterocyclic β-diketone by Schiff-base condensation will further increase coordination sites and facilitate the generation of polynuclear structures.

Objective: A series of β-diketones (2a-2c) containing different heterocycles such as pyridine, thiophene and furan and their corresponding isoxazole compounds (3a-3c) were synthesized.

Materials and Methods: The Claisen condensations were investigated in a solvent-free rheological phase system at room temperature to obtain heterocyclic β-diketones 2a-2c, which further reacted with hydroxylamine hydrochloride to obtain heterocyclic isoxazoles 3a-3c. All these compounds were well characterized by EA, IR, 1H NMR and X-ray crystal diffraction to confirm the structures. Synthetic mechanisms of compounds and the effects of different heterocycles on reactivity were discussed deeply.

Result: 1H NMR indicated that these diketones do not exist as a total diketonic form but an equilibration between diketone and enol forms in CDCl3 solvent, in which the enol form accounts for 98.0% in 2a, 94.3% in 2b, 95.5% in 2c. While crystal structures of 2a-2c showed that the reaction allows to isolate diketones at the solid state. Crystal structures of 3a-3c showed that the neutral β-ketone oximes resonate and cyclize to form the target heterocyclic isoxazoles.

Conclusion: A SN1 nucleophilic substitution mechanism of Claisen ketoester condensation was proposed for the syntheses of 2a-2c, and a SN1 single molecule nucleophilic substitution reaction mechanism was put forwarded for 3a-3c.

Keywords:

Heterocyclic ?-diketone, heterocyclic isoxazole, rheological phase reaction, crystal structure, reaction mechanism.

Affiliation:

College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an



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