The conformational behavior of 2-aryloxytetrahydropyrans and 2-acetoxytetrahydropyran, and barrier to ring inversion was written by Ouedraogo, Adama;Lessard, Jean. And the article was included in Canadian Journal of Chemistry in 1991.Electric Literature of C6H12O2 This article mentions the following:
The 13C NMR data of a series of 2-(4-substituted phenoxy)tetrahydropyrans at 156 K and in CF2Br2 and CHFCl2 solvents show that the axial preference increases with electron withdrawal in the aryloxy group: from 79% (ΔG°E→A = -0.4 kcal mol-1) (4-OCH3) to 90% (ΔG°E→A = -0.7 kcal mol-1) (4-NO2) in CF2Br2. The axial preference (anomeric effect) is smaller in the more polar CHFCl2 solvent, as expected, and the substituent effect is smaller also: change in ΔG°E→A from -0.3 (4-OCH3) to -0.5 (4-NO2) kcal mol-1. However, the axial preference of 2-acetoxytetrahydropyran is shown to be smaller than that of 2-phenoxytetrahydropyran in CF2Br2 solvent although the acetoxy group is expected to be more electroneg. than the phenoxy group. Furthermore, the polarity of the solvent has no effect on the conformational equilibrium of 2-acetoxytetrahydropyran. The results are interpreted in terms of both orbital and electrostatic interactions. The ring-inversion barrier of 2-alkoxy- and 2-aryloxytetrahydropyrans, determined by the temperature-coalescence method, is lower than that of tetrahydropyran by about 1.5 kcal mol-1. In the experiment, the researchers used many compounds, for example, 2-Methoxytetrahydro-2H-pyran (cas: 6581-66-4Electric Literature of C6H12O2).
2-Methoxytetrahydro-2H-pyran (cas: 6581-66-4) belongs to tetrahydropyran derivatives. In organic synthesis, the 2-tetrahydropyranyl group is used as a protecting group for alcohols. The Prins reaction of homoallylic alcohols with aldehydes afforded an alternative method for the preparation of tetrahydropyrans.Electric Literature of C6H12O2
Referemce:
Tetrahydropyran – Wikipedia,
Tetrahydropyran – an overview | ScienceDirect Topics