Stereopure Functionalized Benzosultams via Ruthenium(II)-Catalyzed Dynamic Kinetic Resolution–Asymmetric Transfer Hydrogenation

A highly diastereo- and enantioselective Ru­(II)-catalyzed dynamic kinetic resolution–asymmetric transfer hydrogenation (DKR–ATH) of α-(<i>N</i>-sulfonylimino) and α-(<i>N</i>-sulfonylamino) aryl ketones to 4-hydroxy-benzo-δ- and 3-(α-hydroxy-arylmethyl)-benzo-γ-sultams is presented. By employing enantiopure <i>ansa</i>-Ru­[PipSO<sub>2</sub>DPEN­(CH<sub>2</sub>)<sub>4</sub>Ph] <b>cat. II</b> with S/C = 10 000 in a HCO<sub>2</sub>H/Et<sub>3</sub>N binary mix, up to >99.9% ee and dr >99:1 are obtained with 100% conversion under mild conditions. Application to access the stereopure “structurally simplified TsDPEN” <i>N</i>,<i>N</i>-ligand s<i>yn</i>-3-(α-aminobenzyl)-benzo-γ-sultam (“<i>syn</i>-ULTAM”) and its structural isomer <i>trans</i>-4-amino-3-phenyl-benzo-δ-sultam (<i>trans</i>-<b>4</b>) is demonstrated.