Asymmetric Oxidation of Thioethers .4. Optical Resolution of [1,1'-binaphthalene]-2,2'-dithiol

Almost optically pure (e.e. > 98%) [1,1\u2032-binaphthalene]-2,2\u2032-dithiol (2) is obtained by resolution of racemic 2via the transformation of the sulfidryl functions into the corresponding thioethers 3 which are asymmetrically oxidized to diastereomeric chiral monosulfoxides 4 and then reconverted into 2. The diastereo and enantioselectivity is dependent on the structure of the thioether; i.e. the dimethylthioether 3a gives two diastereomeric sulfoxides 4a in ca. 1:1 ratio, each of them in > 98% e.e., while cyclic dithioethers 3b\u2013d afford a single diastereomeric sulfoxide 4b\u2013d in 46\u201378% e.e.