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-(N-sulfonylimino) and α-(N-sulfonylamino) aryl ketones to 4-hydroxy-benzo-δ- and 3-(α-hydroxy-arylmethyl)-benzo-γ-sultams is presented. By employing enantiopure ansa-Ru­[PipSO2DPEN­(CH2)4Ph] cat. II with S/C = 10 000 in a HCO2H/Et3N 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” N,N-ligand syn-3-(α-aminobenzyl)-benzo-γ-sultam (“syn-ULTAM”) and its structural isomer trans-4-amino-3-phenyl-benzo-δ-sultam (trans-4) is demonstrated.