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, cis- and trans-3,4-disubstituted thiadiazolidines 5 and 6 can enantioselectively be obtained from thiadiazoles 2 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 cis-isomers 5 which, under acidic conditions, undergo a novel isomerization into the trans-isomers 6. These cyclic sulfamides can be transformed into 1,2-diamines as well as 2,3-diamino acids.