Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

A series of tetrahydropyran-2-yl radical (1) analogs was studied using density functional theory (DFT) to model conformational behavior of glycopyranosyl radicals. Calculations of the structure and stability of the ⁴C₁, ¹C₄, B_2,5, ^O,3B, and ⁴H₃ ring conformers for tetrahydropyran-2-yl radical (1) and for 3-fluoro- (2, 7), 3-hydroxy- (3, 8), 3-methoxy- (4, 9), 3-acetoxy- (5, 10), and 3-(benzyloxy)tetrahydropyran-2-yl (6, 11) derivatives showed that conformational behavior of the 3-substituted radicals depends on both the electronic character and orientation of the C3 substituent. The calculations show that radical 1 is slightly pyramidal and exists as an equilibrium mixture of the ⁴C₁ and ¹C₄ conformers. Substituents at the C3 position force 2-11 radicals to adopt a chair conformation with the substituent in the axial orientation. Thus radicals 2-6 prefer the ¹C₄ conformer though there are several ring conformers in equilibrium whereas for radicals 7-11 the ⁴C₁ conformer predominates. The calculated preferences are consistent with available ESR data. These results provide further support for the importance of quasi-homoanomeric interactions on stability of anomeric radicals.

Keywords: Carbohydrates; Radicals; Tetrahydropyrans; Conformational analysis; Quasi-homoanomeric effect; Molecular modeling; DFT calculations; Ab initio; ESR spectroscopy.

References: 32 live references.