Enantioselective Oxidation of Thioethers - A Route To the Resolution of [1,1'-binaphthalene]-2,2'-dithiol

A route to the resolution of racemic [1,1'-binaphthalene]-2,2'-dithiol 2 is described, involving the transformation of 2 into a series of dithioethers. The latter are subjected to asymmetric oxidation to monosulfoxides by a procedure developed in our laboratory. For some of the thioethers examined the oxidation is both highly diastereo- and/or enantioselective. The resolved 2 is then obtained from the optically pure monosulfoxides either by oxidation to the bis-sulfoxides followed by a Pummerer reaction or by a deoxygenation to the dithiother and subsequent reduction. In both cases enantiomerically pure 2 (e.e. > 98%) was obtained.