Stereoelectronic Control in the Gas-Phase Ionization of Cyclic Ortho Esters

Article abstract of DOI:10.1021/ja00412a029

As a test of stereoelectronic control in the gas phase, the rates of ionic cleavage of the exocyclic methoxyl group of 2-methoxy-cis-4,6-dimethyl-1,3-dioxane diastereomers have been measured by ion cyclotron resonance techniques.The reactant ions were isopropyl and (methylthio)methyl cations derived from electron impact cleavage of 2-methylpropane and 2-(methylthio)ethanol, respectively.Within experimental error, the rates of cleavage of the equatorial methoxyl were the same as those of the axial methoxyl with a given reactant ion.With use of mixtures of deuterium-labeled and unlabeled diastereomers and reactant ions derived from isopropyl ether and acetylacetone, a slight (10percent) preference was seen for cleavage of the axial methoxyl group.The significance of these results in terms of stereoelectronic and conformational effects is discussed.