Dimethyl itaconate, asymmetric hydrogenation

Reaction Characteristics of Immobilized Ru-BINAP Catalysts in Asymmetric Hydrogenation of Dimethyl itaconate... 

In this work, various Ru-BINAP catalysts immobilized on the phosphotungstic acid(PTA) modified alumina were prepared and the effects of the reaction variables (temperature, H2 pressure, solvent and content of triethylamine) on the catalytic performance of the prepared catalysts were investigated in the asymmetric hydrogenation of dimethyl itaconate (DMIT). 

Effect of reaction conditions on the asymmetric hydrogenation of dimethyl itaconate over immobilized Ru-BINAP catalyst... 

A 1996 work deposited four different catalytic metals on a p-cyclodextrin— epichlorohydrin copolymer to prepare Pd(Pt, Rh, Ru)-P-cyclodextrin copolymer catalysts.8 These were used to catalyze the asymmetric hydrogenations of the C=C bonds of trans-2-methyl-2-pentenoic acid, and dimethyl itaconate. 

Table 7 Asymmetric hydrogenation of itaconic acid or dimethyl ester...

If Q-symmetric ligands are employed in asymmetric hydrogenation instead of the corresponding C2-symmetric ligands, there coexist principally four stereoiso-meric substrate complexes, namely two pairs of each diastereomeric substrate complex. Furthermore, it has been shown that, for particular catalytic systems, intramolecular exchange processes between the diastereomeric substrate complexes should in principle be taken into account [57]. Finally, the possibility of non-estab-hshed pre-equilibria must be considered [58]. The consideration of four intermediates, with possible intramolecular equilibria and disturbed pre-equihbria, results in the reaction sequence shown in Scheme 10.3. This is an example of the asymmetric hydrogenation of dimethyl itaconate with a Rh-complex, which contains a Q-symmetrical aminophosphine phosphinite as the chiral ligand. 

The hydrogen consumption and enantioselectivities for the asymmetric hydrogenation of dimethyl itaconate with various substituted catalysts of the basic type [Rh(PROPRAPHOS)COD]BF4 are illustrated in Figure 10.13 [61]. The systems are especially suitable for kinetic measurements because of the rapid hydrogenation of COD in the precatalyst. There are, in practice, no disturbances due to the occurrence of induction periods. 

Table 10.2 Kinetic analysis of the asymmetric hydrogenation of dimethyl itaconate with derivatives of [Rh(PROPRAPHOS)-COD]BF4 (see Fig. 10.13).

Fig. 10.17 Asymmetric hydrogenation of dimethyl itaconate with [Rh(Ph-j8-glup-OH)(MeOH)2]BF4 comparison between first-order fit (x-axis) and experimental values. Conditions 0.01 mmol catalyst 1.0 mmol substrate 15.0 mL MeOH 1.013 bar total pressure.

An unusual carbene-thioether hybrid ligand 174 was synthesized and applied in the rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate by Chung and co-workers however, the selectivity and activity were low (Table 27.7, entry 34) [135]. 

When a commercially available C2-symmetric l,4 3,6-dianhydro-D-mannite 29 is chosen as the backbone, reaction of this diol compound with chlorophos-phoric acid diaryl ester gives a series of phosphorate ligands 30. These were tested using the asymmetric hydrogenation of dimethyl itaconate as a model... 

Recently Togni et al. [19] focussed on the preparation of asymmetric dendrimer catalysts derived from ferrocenyl diphosphine ligands anchored to dendritic backbones constructed from benzene-1,3,5-tricarboxylic acid trichloride and adamantane-l,3,5,7-tetracarboxylic acid tetrachloride (e.g. 11, Scheme 11). In situ catalyst preparation by treatment of the dendritic ligands with [Rh(COD)2]BF4 afforded the cationic Rh-dendrimer, which was then used as a homogeneous catalyst in the hydrogenation reaction of, for example, dimethyl itaconate in MeOH. In all cases the measured enantioselectivity (98.0-98.7%) was nearly the same as observed for the ferrocenyl diphosphine (Josiphos) model compound (see Scheme 11). 

The term chiral poisoning as a deactivating strategy has been proposed for the asymmetric hydrogenation reaction of dimethyl itaconate catalyzed by CHIRAPHOS-Rh complex (Scheme 8.5). The combination of racemic CHIRAPHOS-Rh complex and (5)-METHOPHOS 6 as a catalyst poison yields the hydrogenated product in 49% ee. (5)-METHOPHOS is believed to bind to the (S. S -CHlRAPHOS-Rh complex preferentially, as the use of enantiopure (R,R)-CHlRAPHOS-Rh complex affords the product with 98% ee. 

In contrast to the many examples of asymmetric hydrogenation of the parent itaconic acid or its dimethyl ester, very few ligands have been reported for the enantioselec-... 

The dynamic behavior of the model intermediate rhodium-phosphine 99, for the asymmetric hydrogenation of dimethyl itaconate by cationic rhodium complexes, has been studied by variable temperature NMR LSA [167]. The line shape analysis provides rates of exchange and activation parameters in favor of an intermo-lecular process, in agreement with the mechanism already described for bis(pho-sphinite) chelates by Brown and coworkers [168], These authors describe a dynamic behavior where two diastereoisomeric enamide complexes exchange via olefin dissociation, subsequent rotation about the N-C(olefinic) bond and recoordination. These studies provide insight into the electronic and steric factors that affect the activity and stereoselectivity for the asymmetric hydrogenation of amino acid precursors. 

Kollner et al. (29) prepared a Josiphos derivative containing an amine functionality that was reacted with benzene-1,3,5-tricarboxylic acid trichloride (11) and adamantane-l,3,5,7-tetracarboxylic acid tetrachloride (12). The second generation of these two types of dendrimers (13 and 14) were synthesized convergently through esterification of benzene-1,3,5-tricarboxylic acid trichloride and adamantane-1,3,5,7-tetracarboxylic acid with a phenol bearing the Josiphos derivative in the 1,3 positions. The rhodium complexes of the dendrimers were used as chiral dendritic catalysts in the asymmetric hydrogenation of dimethyl itaconate in methanol (1 mol% catalyst, 1 bar H2 partial pressure). The enantioselectivities were only... 

Table 2.1 Asymmetric hydrogenation of dimethyl itaconate (A) and methyl (Z)-ot-acetamido cinnamate (B)...

Asymmetric hydrogenation of dimethyl itaconate and methyl (Z)-a-acetamido cinnamate with in situ formed rhodium(I)-diphosphinite catalyst system gave the desired products with high activity and enantioselectivity (Table 2.1). The asymmetric hydrogenation may be applied to a wide range of substrates. 

The new ligands were evaluated in the Rh-catalyzed asymmetric hydrogenation of benchmark substrates methyl a-N-acetamidoacrylate (7), methyl a-(2)-N-acetamidocinnamate (8) and dimethyl itaconate (9) (Table 2.3). For all three substrates, catalyst performance was superior in CH2CI2. Differences of up to 83% ee compared to otherwise identical reactions conducted in MeOH could be noted, giving... 

Figure 8.12 U rea functionalized phosphate ligands for asymmetric hydrogenation of dimethyl itaconate (DMI), N-(3,4-dihydronaphthalen-2-yl)acetamide (DNA) and methyl 2-acetamidoacrylate (MAA).

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