Synthesis of substituted tetrahydropyran-4-one and its oxime

Abstract

Tetrahydropyranone derivatives are promising starting materials for the synthesis of various heterocyclic compounds with biological activity. Oximes obtained on the basis of heterocyclic compounds, which include 3,5-substituted tetrahydropyran-4-one, possess antibacterial activity. We studied the optimal conditions for the synthesis of 3,5 substituted tetrahydropyran-4-one and its oxime, to confirm the obtained structures, and to perform quantum-chemical calculations of the conformations of the target compounds. The optimal method for the 3,5-dimethyleneoxytetrahydropyran-4-one (III) synthesis was the condensation of acetone with formaldehyde in a ratio of 1 : 4  in the presence of K₂CO₃; the yield was 67.4 %. The reaction of (III) with hydroxylamine hydrochloride was studied in the presence of NaOH and AcONa at different temperatures. The optimal yield (65.3%) of the product (IV) was obtained in the presence of AcONa whit heating below 80 ⁰C. To determine the composition of obtained compounds elemental analysis was used. Functional composition and structural elements were identified using IR spectroscopy. To prove the structure of the synthesized oxime, ¹H and ¹³C NMR spectra were taken on a JNN-ECA Jeol 400 spectrometer (at a frequency of 399.78 MHz and 100.53 MHz) with a CDCl₃ solvent. Quantum-chemical calculations of stable conformations of (III) and (IV) was performed using ab initio DFT B3LYP method and 6-31G (d) and 6-311+G(3df,2p) basis sets. Calculated total energies and dipole moments allow to find the geometry of the most stable conformers. The most stable conformer of (IV) is the 3a5a configuration of substituents, which can be explained by the formation of intramolecular hydrogen bonds. Calculations show that the syn- and anti-isomers of 3,5-dimethyleneoxytetrahydropyran-4-one oxime are energetically equivalent.