Asymmetric transfer hydrogenation aromatic

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... 

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... 

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... 

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

A class of simple, modular, and highly efficient a-amino acid amides ligands for Ru-and Rh-catalysed asymmetric transfer hydrogenation of aromatic ketones in propan-2-ol has been developed. A remarkable feature with these ligands is the switch of product enantioselectivity observed when the amide functionality is replaced by the corresponding thioamide. The results obtained have significant mechanistic implications... 

J. Gao, T. Ikariya, and R. Noyori, Aruthe-niumjii) complex with a C2-symmetric diphosphine/diamine tetradentate ligand for asymmetric transfer hydrogenation of aromatic ketones, Organometallics 1996, 15, 1087-1089. 

Phosphoric acid catalysts, bearing bulky groups, have been devised for the asymmetric transfer hydrogenation of imines with Hantsch ester. With the catalyst (14), (g) enantioselectivity up to 93% has been achieved in the reduction of aromatic imines. 

A method for the monoarylation of (15,25)-l,2-diaminocyclo-hexane by means of palladium-catalyzed aromatic amination has been recently described (eq 13). The resulting new ligands were tested in the catalytic asymmetric transfer hydrogenation of acetophenone. 

An alternative approach is the use of a PS support bearing sulfonate pendant groups. For this, a quaternary ammonium salt of styrenesulfonic acid was copolymerized with a N-(p-styrenesulfonyl)-l,2-diphenylethylenediamine monomer. The polymeric chiral Ru complex was prepared from 177 and [RuCl2(p-cymene)]2 and applied to the asymmetric transfer hydrogenation of aromatic ketones in water (Scheme 3.55) [114]. The polymeric chiral complex was evenly suspended in water and the reaction proceeded smoothly to produce the alcohol in quantitative yield and with high enantioselectivity. For several of the aromatic ketones tested, higher... 

The past 35 years have seen both the asymmetric hydrogenation and asymmetric transfer hydrogenation of imines develop into useful methods for the synthesis of chiral amines. Particularly, focused research over the past 15 years has led to highly enantioselective examples of both reaction types and has added aza aromatics, activated imines, and iminium cations to their purview. In addition, the asymmetric hydrogenation and asymmetric transfer hydrogenation of imines have both been apphed to total syntheses. Because they are necessarily isomeri... 

The asymmetric transfer hydrogenation of aromatic ketones catalysed by organometallic complexes of chiral A-tosylated diamines has been reviewed." ... 

Complexes (240) and (241) were used to catalyse transfer hydrogenation and asymmetric transfer hydrogenation of various aromatic ketones. The transfer hydrogenation reaction gave corresponding alcohols in quantitative yield, which is attributed to the establishment of an unsymmetrical environment around the Ru(II) by two different... 

The efficiency of synthesized chiral azolium salts (260)-(262), derived from (5)-pyroglutamic acid, as carbene precursors was evaluated in the [Rh(cod)Cl]2-catalysed asymmetric transfer hydrogenation of aromatic ketones in isopropanol, acting as the hydrogen donor, and KOH as promoter to the corresponding alcohol. It was reported that the use of (262) displayed the highest activity and asymmetric induction for the transfer hydrogenation. The yield was up to 94% and enantioselectivities up to 90% ee were observed. ... 

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