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

Abstract

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[PipSODPEN(CH)Ph] cat. II with S/C = 10 000 in a HCOH/EtN 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.

Stabilising fleeting intermediates of stilbene photocyclization with amino-borane functionalisation: the rare isolation of persistent dihydrophenanthrenes and their [1,5] H-shift isomers

“…All starting materials were purchased from Energy Chemical. (Pyridin-2-ylmethyl)triphenylphosphonium chloride, 9 2-metho-xybenzyltriphenylphosphonium chloride, 10 benzylphosphonium bromide, 11 2-thienylmethyltriphenylphosphonium chloride, 12 3-thienylmethyltriphenylphosphonium bromide, 13 2-dimesityl-borylbenzaldehyde, 22 2-bromo-4-(dimethylamino)benzalde-hyde, 23 and 5-bromo-2-(dimethylamino)benzaldehyde 24 were synthesized according to procedures reported in literature. The starting materials for E -8a and E -9a ( BO1′ and BO1m , respectively) were prepared according to procedures outlined in the ESI.…”

Escaping from Flatland: Stereoconvergent Synthesis of Three‐Dimensional Scaffolds via Ruthenium(II)‐Catalyzed Noyori–Ikariya Transfer Hydrogenation

“…To obtain the former ( 79 ) in quantitative yield, it was important to stir the isomeric mixture of iminoketones 77 and 78 in HCO 2 H/Et 3 N before adding the catalyst during which time a partial (uncatalyzed) reduction and ring expansion occurred. Stereopure benzo‐γ‐sultam 80 was prepared using EtOH as a cosolvent with a higher loading of ( S , S )‐ K present from the start, kinetically disfavoring ring expansion of the mono‐reduced species [36] …”

Recent Progress and Applications of Transition-Metal-Catalyzed Asymmetric Hydrogenation and Transfer Hydrogenation of Ketones and Imines through Dynamic Kinetic Resolution

“…Mohar and co-workers showed that the chiral ansa-Ru(II) complex (S,S)-CAT4 was an effective catalyst for the ATH of -(sulfonylimino) and -(sulfonylamino) aryl ketones under DKR conditions (Scheme 57). 70 Notably, this protocol was performed at 60 °C in a HCO 2 H/Et 3 N (3:2) binary mixture under a low catalyst loading of S/C = 10000, giving optically active 4-hydroxy-1,2,3,4-tetrahydro-1,2benzothiazine S,S-dioxides with two contiguous stereogenic centers in 97-100% isolated yield with up to >99.9% ee and consistently high levels of cis diastereofacial selectivity.…”