Stereochemistry of sulphur organic compounds. Part 24. Synthesis and conformational analysis of cis- and trans-2-methoxy-5-methylthio derivatives of oxane

Abstract

The synthesis and conformational analysis of cis- and trans-2-methoxy-5-X-oxane, by ¹³C n.m.r. at low temperature in several solvents, are reported. ΔG° Values in CD₂Cl₂ of trans-isomers are –0.61 (X, SMe), +1.65 (X, SOMe more polar isomer), +0.57 (X, SOMe less polar isomer), –0.50 (X, SO₂Me), and +1.4 (X, ⁺SMe₂) kcal mol^–1, negative values indicating a preference for the diequatorial conformer. In all cis-compounds only one conformation is present. By comparison of these values with those calculated from 2-methoxyoxane and 3-methylthio derivatives of oxane the role played by the anomeric effect on the (oxygen–sulphur)_1,2-g interaction can be inferred.