Enantioselective Synthesis of 3,4-Disubstituted <i>cis</i>- and <i>trans</i>-1,2,5-Thiadiazolidine-1,1-dioxides as Precursors for Chiral 1,2-Diamines

Both, <i>cis</i>- and <i>trans</i>-3,4-disubstituted thiadiazolidines <b>5</b> and <b>6</b> can enantioselectively be obtained from thiadiazoles <b>2</b> which, in turn, are efficiently prepared from the respective 1,2-diketone by an improved protocol. An asymmetric ruthenium-catalyzed transfer hydrogenation followed by a diastereoselective hydride addition furnishes exclusively the <i>cis</i>-isomers <b>5</b> which, under acidic conditions, undergo a novel isomerization into the <i>trans</i>-isomers <b>6</b>. These cyclic sulfamides can be transformed into 1,2-diamines as well as 2,3-diamino acids.