The “Reverse‐Tethered” Ruthenium(II) Catalyst for Asymmetric Transfer Hydrogenation: Further Applications.

Abstract

Hydrogenation O 0220The "Reverse-Tethered" Ruthenium(II) Catalyst for Asymmetric Transfer Hydrogenation: Further Applications. -It is found that the title catalyst (RTC) efficiently promotes the asymmetric hydrogenation of various aromatic and heteroaromatic ketones. However, starting from aliphatic ketones only moderate to low enantioselectivity is achieved. -(MORRIS, D. J.; HAYES, A. M.; WILLS*, M.; J. Org. Chem. 71 (2006) 18, 7035-7044; Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UK; Eng.) -Jannicke 01-052

Synthesis and use of an asymmetric transfer hydrogenation catalyst based on iron(II) for the synthesis of enantioenriched alcohols and amines

“…Finally tethered Noyori-type catalysts like C have been developed by Wills and coworkers. [15][16][17] They are best used with triethylamine/formic acid mixture as solvent to drive the reductions to completion, making product separation more challenging than from the isopropanol solutions used in the iron catalysis. Again the enantioselectivity of ketone reduction, where comparisons are available (entries 1, [11][12][13], are higher for the ruthenium catalyst but the activity is much lower, reductions taking many hours compared to minutes for Fe.…”

Ru‐TsDPEN catalysts and derivatives in asymmetric transfer hydrogenation reactions

“…Further depending on interaction of substrate and catalyst, various substrate has been studied for understanding electronic effect of substituents in ATH process. Among phenoxy v/s alkoxy group (like -OMe, -O n Bu, -O i Pr, -OAllyl), variation in enantioselectivity of the reduced product with (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40) %ee (Scheme 5) has been observed. Further transition state of all determined configuration of synthesized product has been confirmed where it is clear that more electron-rich Further, electronically deficient group like -OpClC 6 H 4 /-OPh shows product formation with merely 6%ee (25).…”

“…After this, two aryloxy group which showed steric hinderance were used as substituents like in compound 30, where 2,6-dimethoxyphenoxy group is present along with -O i Pr showed enantioselectivity with only 16%ee, further when -O i Pr is replaced by -OPh group (compound 34), then % ee increases to 42%, similarly with -OC 6 H 4 p(OMe) it again showed a decreases in %ee (compound 31) (Scheme 7). It is because of 2,6-dimethoxyphenoxy group which dominates over both -OPh group (34) and -OC 6 H 4 p(OMe) group (31), ultimately leading to C (alkyl)-O bond not to be in coplanar state with aromatic ring. Thus.…”

“…Tethering between η 6 -arene and heteroatom of chelating ligand makes it rigid, thus prevents the rotation of η 6 -arene, thereby renovating the catalyst with functional group in such a way that it modifies its catalytic property. [32][33][34][35][36][37][38] Owing to its unique nature, catalyst with tethering-unit has been extensively used for ATH process.…”

Bifunctional Homogeneous Catalysts Based on Ruthenium, Rhodium and Iridium in Asymmetric Hydrogenation

“…First introduced by Wills and co-workers, this new family of catalysts exhibited enhanced catalytic performances and stability (Scheme 2). [39][40][41][42] Scheme 2. ATH of -chloroketones with a diamine tethered arene ruthenium catalyst.…”