Collect. Czech. Chem. Commun.
1981, 46, 2912-2923
https://doi.org/10.1135/cccc19812912
Mixed aromatic-aliphatic acetals; Their preparation, 1H and 13C-NMR spectra and hydrogenolysis by ethereal solution of chloroalane
Jiří Dušeka, Vladimír Sklenářb and Jaroslav Jonasc
a Research Institute of Pure Chemicals, Lachema, Brno
b Institute of Instrumental Technique, Czechoslovak Academy of Sciences, Brno
c Department of Organic Chemistry, Purkyně University, 611 37 Brno
Abstract
The corresponding p-X-phenylisobutyl acetals to acetaldehyde (I), 2-(p-X-phenoxy)tetrahydropyrans (II), 2-(p-X-phenoxy)tetrahydrofurans (III), and cyclohexyl(p-X-phenyl)acetals of acetaldehyde (IV) were prepared by addition of p-X-substituted phenols to isobutyl vinyl ether, 2,3-dihydro-4H-pyran, 2,3-dihydrofuran, and cyclohexyl vinyl ether, respectively. The structures of acetals I-IV were confirmed by their 1H and 13C NMR spectra. Diastereotopic protons of the methylene and geminal methyl groups are anisochronous in the 1H NMR spectra of acetals I. 13C NMR spectra of acetals IV demonstrate anisochronous behaviour of cyclohexane ring diastereotopic carbon atoms. The constants σp+ for several groups calculated using 13C NMR spectra are: 1-isobutoxy-1-ethoxy- (-0.56), 2-tetrahydropyranyloxy- (-0.58), 2-tetrahydrofuryloxy- (-0.59), and 1-cyclohexyloxy-(1-ethoxy) (-0.57). Experimental relative rate constants of hydrogenolysis of acetals I and II by ethereal solution of chloroalane yield best correlations with σp+ constants of the substituent X, providing the values ρ = 2.61 and ρ = -1.09 for compounds of the series I and II, respectively. The importance of these results for finding the rate determining step of the studied reaction is discussed.
