Enantioselective hydrogenation of dimethyl itaconate

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... 

Several diphosphine ligands have been applied and the corresponding complexes have been tested for the immobilization (Fig. 2.1.6.3). The activity of different free and immobilized complexes in the enantioselective hydrogenation of dimethyl itaconate and methyl a-acetamidoacrylate was investigated. In blank reactions over pure mesoporous materials no reaction took place. When rhodium supported on carriers was used as catalyst, no enantiomeric excess was observed. 

The continuous enantioselective hydrogenations of dimethyl itaconate (DMI) with Ru-BINAP (MW = 929 Da) and of methyl 2-acetamidoacrylate (MAA) with... 

Figure 12.9 Enantioselective hydrogenation of dimethyl itaconate. (Adapted from Ref. [20].)...

Figure 12.11 The results from continuous enantioselective hydrogenation of dimethyl itaconate at 40 °C under 120 bar using the flow rate of 85 and 10 ml min for CO2 and H2, respectively. Symbols conversion (A), enantioselectivity ( ] and cumulative TONs ( ) using (Sa,Rc)-l-naphtyl-...

Hintermair et al. [56] also published the continuous enantioselective hydrogenation of dimethyl itaconate using a chiral rhodium SILP catalyst under scCOj flow (Figure 18.10). 

The chiral poisoning strategy has also been developed by Faller in the KR ofa mixture of enantiomeric rhodium complexes by a chiral ligand in the enantioselective hydrogenation of dimethyl itaconate [100]. 

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... 

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. 

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. 

This catalyst showed high enantioselectivity in the hydrogenation of dimethyl itaconate. The best enantioselectivities (83-89% ee) were obtained in ethanol as... 

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... 

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. 

Polymeric membranes also show potential for application in the area of chiral catalysis. Here metallocomplexes find use as homogeneous catalysts, since they show high activity and enantioselectivity. They are expensive, however, and their presence in the final product is undesirable they must be, therefore, separated after the reaction ends. Attempts have been made to immobilize these catalysts on various supports. Immobilization is a laborious process, however, and often the catalyst activity decreases upon immobilization. An alternative would be a hybrid process, which combines the homogeneous catalytic reactor with a nanofiltration membrane system. Smet et al. [2.98] have presented an example of such an application. They studied the hydrogenation of dimethyl itaconate with Ru-BINAP as a homogeneous chiral catalyst. The nanofiltration membrane helps separate the reaction products from the catalyst. Two different configurations can be utilized, one in which the membrane is inserted in the reactor itself, and another in which the membrane is extraneous to the reactor. Ru-BINAP is known to be an excellent hydrogenation catalyst... 

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