Hydrogenation itaconate, dimethyl

In order to prove that the reaction was catalyzed heterogeneously and to exclude the possibility of leaching and homogeneous catalysis, hot filtration tests were performed [44]. For the dimethyl itaconate hydrogenation, removal of the COD-RhDuphos immobilized on Al-SBA-15 effectively stopped the reaction after 5 h. After 24 h, the conversion of the filtered sample remained at 40%, whereas the original batch with catalyst was converted completely (Fig. 2.1.6.4). 

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... 

Short residence time and high heat transfer capabilities are demanded for the transfer hydrogenation of dimethyl itaconate, as in general for comparable liquid/liquid reactions [117]. 

On the other hand, Bolm et al. have reported, more recently, the use of BINOL-derived A -phosphino sulfoximines as ligands in the rhodium-catalysed hydrogenation of dimethyl itaconate and a-acetamidoacrylates, achieving excellent enantioselectivities of up to 99% ee (Scheme 8.12). In the main... 

Table 24.1. Enantioselective hydrogenation of dimethyl itaconate using Rh(l)-complexes ...

Togni and co-workers have used the convergent methodology to link phosphine-containing chiral ferrocene ligands on the cyclophosphazene core to obtain dendrimeric structures of the type 37 (Fig. 21) (201). The reaction with the cyclophosphazene end occurs by the replacement of the P-Cl bond and by the formation of the P-0 bond. The dendrimers contain twelve and sixteen ferrocene moieties respectively. The phosphine units present can coordinate to Rh(I) to afford metallic dendrimers, which have been shown to be excellent catalysts for the enantioselective hydrogenation of dimethyl itaconate. The product... 

The aqueous biphase hydrogenation of dimethyl itaconate is accomplished with an Ir-(7 )-(7 )-3-benzyl(/>-sulfonate)-2,4-bis(diphenylphosphino)pentane complex.605... 

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. 

A set of core-functionalized dendrimers was synthesized by Van Leeuwen et al. and one compound was applied in continuous catalysis. [45] The dendritic dppf, Xantphos and triphenylphosphine derivatives (Figures 4.22, 4.30 and 4.31) were active in rhodium-catalyzed hydroformylation and hydrogenation reactions (performed batch-wise). Dendritic effects were observed which are discussed in paragraph 4.5. The dendritic rhodium-dppf complex was applied in a continuous hydrogenation reaction of dimethyl itaconate. 

Fu has reported a planar-chiral bisphosphorus ligand 45 with a phosphaferrocene backbone. The ligand has provided enantioselectivity up to 96% ee in the hydrogenation of a-dehydroamino acid derivatives.99 Another planar-chiral ferrocene-based bisphosphorus ligand 46 has been reported by Kagan recently and enantioselectivity up to 95% ee has been obtained in the reduction of dimethyl itaconate.100... 

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. 

A comparison of the activities for various catalyst derivatives shown in Figure 10.13 seems to prove that the ligand with the cyclohexyl residue leads to the most active catalyst for the hydrogenation of dimethyl itaconate. The catalyst containing the methyl derivative apparently exhibits the lowest activity. 

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

Fig. 10.16 Variation of the concentration of dimethyl itaconate for the hydrogenation with [Rh((S)-PROPRAPHOS)COD]BF4.

These results, obtained from the gross-hydrogen consumption under normal conditions on the basis of the model developed above, make it clear that even catalysts of the same basic type can give rise to considerably different pre-equilibria. As a consequence, comparison of activities of various catalytic systems under standard conditions can provide the wrong picture. Hence, the cyclohexyl precatalyst with dimethyl itaconate seems to be the most active one (by reference to Fig. 10.13). Nonetheless, an increase in the initial substrate concentration by a factor of ten already leads to a different order in activity. 

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.

Borner reported the synthesis of pyrophosphites 149 with chiral binaphthyl substituents [118]. The results showed that the Hg-binaphthyl unit was the best for the Rh-catalyzed hydrogenation of methyl (Z)-2-acetamidocinnamate (48% ee) and dimethyl itaconate (70% ee). 

In 1982, Yamashita reported the application of L-talopyranoside-based phos-phine-phosphinite ligand 165 (Fig. 27.15), and found that it induced low enan-tioselectivity (4.7-13% ee) in the hydrogenation of a-acetamidocinnamic acid [119]. Reetz introduced the phosphine-phosphonite ligand (151-153), which led to moderate enantioselectivity (52-88% ee) in the Rh-catalyzed hydrogenation of dimethyl itaconate [120]. The binaphthyl unit remained an essential element in the system. 

Pizzano and Suarez described a convenient preparation of a series of new chiral phosphine-phosphites based on the easy demethylation of o-anisyl phosphines [124]. Rh-156a complex was found to be the most effective catalyst for the hydrogenation of dimethyl itaconate (99.6% ee), whereas 155b and 156a induced >99% ee in the hydrogenation of methyl N-2-acetamidocinnamate. Reetz... 

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]. 

Very recently, Reetz, Ma and Goddard reported phosphoramidites based on BINOL bearing a single ortho-substituent (Scheme 28.10) [69]. These ligands are also chiral on phosphorus, such that the synthesis results mostly in diastereo-mers which have to be separated. In several cases, however, one of the diaster-eomers was formed exclusively. Some of the ligands afford high ee-values in the hydrogenation of methyl N-acyl dehydroalanine and dimethyl itaconate. 

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