Asymmetric hydrogenation aromatic ketones

A chiral catalyst consisting of Irans-RuC]2(xy]binap)(daipen) and (CH3)3COK in 2-propanol effects asymmetric hydrogenation of a-, / -, and y-amino aromatic ketones [128]. Hydrogenation of 2-(dimethylamino)acetophenone catalyzed by the (R)-XylBINAP/(R)-DAIPEN-Ru complex [(R,R)-31D] gives the R amino alcohol in 93% ee (Fig. 32.36). The optical yield is increased up to 99.8%, when... 

On the other hand, one of the first chiral sulfur-containing ligands employed in the asymmetric transfer hydrogenation of ketones was introduced by Noyori el al Thus, the use of A-tosyl-l,2-diphenylethylenediamine (TsDPEN) in combination with ruthenium for the reduction of various aromatic ketones in the presence of i-PrOH as the hydrogen donor, allowed the corresponding alcohols to be obtained in both excellent yields and enantioselectivities, as... 

Hu, A.G., Yee, G.T. and Lin, W.B. (2005) Magnetically recoverable chiral catalysts immobilized on magnetite nanopartides for asymmetric hydrogenation of aromatic ketones. Journal of the American Chemical Society, 127 (36), 12486-12487. 

Table 19 Asymmetric hydrogenation of simple aromatic ketones... 

I. S. 3/ >.4/ >j-2-AZANORBORNYLMETIIANOL, AN EFFICIENT LIGAND FORRUTHENIUM-CATALYSED ASYMMETRIC TRANSFER HYDROGENATION OF AROMATIC KETONES... 

The procedure is very easy to reproduce and the asymmetric transfer hydrogenation may be applied to a wide range of aromatic ketones. Table 9.3 gives different substrates that can be reduced with the Ru(II)-(2-azanorbornylmetha-nol) complex in Ao-propanol... 

R)-BINAP/l,2-diphenylethylenediamine ruthenium(II) complexes covalently attached to polystyrene (Scheme 4.32) promote the asymmetric hydrogenation of aromatic ketones and of a, yS-unsaturated ketones [125]. The catalysts (52) and (53) were reused at high substrate/catalyst molar ratio (S/C) of 2470 in 14 experiments. Remarkably, the enantiopurity of the products remained high after each run, constantly being in the range of 97 to 98% ee. 

Finally, the asymmetric hydrogenation of a series of a-hydroxy aromatic ketones in methanol catalyzed by Cp lr(OTf)(MsDPEN) (42, MsDPEN = N-(methanesul-... 

Table 4.8 Asymmetric transfer hydrogenation of aromatic ketones, catalyzed by [lrH(CO)(PPh3)3]/83 under base-free conditions.

Mashima and Tani et al., and employed in the asymmetric transfer hydrogenation of aromatic ketones [39, 40],... 

The treatment of [Cp MCl2]2 (M = Rh and Ir) with (S,S)-TsDPEN gave chiral Cp Rh and Cp Ir complexes (12a and 12b Scheme 5.9). An asymmetric transfer hydrogenation of aromatic ketones using complex 12 was carried out in 2-propanol in the presence of aqueous KOH (1 equiv.) the results obtained are summarized in Table 5.4. In all of the reactions, the (S)-alcohols were obtained with more than 80% enantiomeric excess (ee) and in moderate to excellent yields. The rhodium catalyst 12a was shown to be considerably more active than the iridium catalyst... 

Ikariya and Noyori et al. also reported the synthesis of new chiral Cp Rh and Cp Ir complexes (13 and 14) bearing chiral diamine ligands [(R,R)-TsCYDN and (R,R)-TsDPEN] (Scheme 5.10) these are isoelectronic with the chiral Ru complex mentioned above, and may be used as effective catalysts in the asymmetric transfer hydrogenation of aromatic ketones [42], The Cp Ir hydride complex [Cp IrH(R,R)-Tscydn] (14c) and 5-coordinated amide complex (14d), both of which would have an important role as catalytic intermediates, were also successfully prepared. 

Table 5.5 Asymmetric transfer hydrogenation of aromatic ketones catalyzed by preformed chiral catalysts and KO Bu system in 2-propanol. ...

Analogous water-soluble Cp Rh and Cp lr complexes were prepared by Williams et al., and used in the asymmetric transfer hydrogenation of aromatic ketones under aqueous conditions [43]. These catalyst complexes contain water-soluble chiral diamine ligands (Scheme 5.11), and were prepared in situ by reacting [Cp MCl2]2 (M = Rh, Ir) with ligands 15a or 15b in the presence of a base, and used immediately. The results of the asymmetric transfer hydrogenation of... 

As shown in Figure 1.26, a chiral Sm(III) complex catalyzes asymmetric reduction of aromatic ketones in 2-propanol with high enantioselectivity. Unlike other late-transition-metal catalysis, the hydrogen at C2 of 2-propanol directly migrates onto the carbonyl carbon of substrate via a six-membered transition state 26A, as seen in the Meerwein-Ponndorf-Verley reduction. ... 

The asymmetric hydrogenation of unfunctionalized ketones is a much more challenging task than that of functionalized ketones [3 j, 115]. Many chiral catalysts which are effective for functionalized ketones do not provide useful levels of enantioselectivity for unfunctio-nalized ketones, due to a lack of secondary coordination to the metal center. Zhang demonstrated the enantioselective hydrogenation of simple aromatic and aliphatic ketones using the electron-donating diphosphane PennPhos, which has a bulky, rigid and well-defined chiral backbone, in the presence of 2,6-lutidine and potassium bromide [36]. 

Aromatic Ketones The DIOP-Rh [116] and DBPP-Rh [117] complexes, in conjunction with a tertiary amine, have been employed in the asymmetric hydrogenation of acetophenone, albeit with moderate enantioselectivity (80 and 82% respectively Tab. 1.10). The asymmetric hydrogenation of aromatic ketones was significantly improved by using the Me-PennPhos-Rh complex, with which enantioselectivities of up to 96% ee were achieved [36]. Interestingly, the additives 2,6-lutidine and potassium bromide were again found to be crucial for optimum selectivity, although their specific role has not been determined. 

Remarkable activity and enantioselectivity in asymmetric hydrogenation of aromatic ketones were reported when ionic liquids were used as solvents for a rhodacarborane catalyst precursor having an alkene ligand, [closo-l,3 p-(ri -3-CH2= CHCH2CH2) -3-H-3-PPh3-3,l,2-RhC2B9Hio] 215). In ionic liquids... 

Ruthenium-Catalyzed Asymmetric Hydrogenation of Aromatic Ketones... 

REGIO- AND STEREO-CONTROLLED OXIDATIONS AND REDUCTIONS Table 3.9 Asymmetric transfer hydrogenation of aromatic ketones 18a-c ... 

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