Itaconic acid hydrogenation

Although the asymmetric hydrogenation of itaconic acid derivatives is a potential synthetic approach to many useful product [105], lower enantioselectivities are often reported. In contrast with other catalysts, f-Bu-BisP, Ad-BisP, t-Bu-MiniPHOS, BIPNOR 27, and Brown s ligand 25 gave high to almost perfect ees in the hydrogenation of these substrates (Scheme 23) [101]. 

Scheme 23. Rh-catalyzed asymmetric hydrogenation reactions of itaconic acid derivatives...

Bidentate chiral bis(aminophosphanes) such as 55-57 (Scheme 44) have been used for the Rh(I)-cataIyzed asymmetric hydrogenation of itaconic acid... 

The formation of a stable hydrogen-bonded ring structure as in poly(itaconic acid) and in poly(maleic acid) has also been shown to affect hydration states (Muto, Komatsu Nakagawa, 1973 Muto, 1974). 

Poly(acrylic acid) is very soluble in water as are its copolymers with maleic and itaconic acids. Solutions of 50 % by mass are easily obtained. The isomer of PAA, poly(ethylene maleic acid), is not so soluble. However, solutions of PAA tend over a period of time to gel when their concentration in water approaches 50 % by mass (Crisp, Lewis Wilson, 1975) this is attributed to a slow increase in the number of intermolecular hydrogen bonds. Copolymers of acrylic acid and itaconic acid are more stable in solution and their use has been advocated by Crisp et al. (1975, 1980). 

In addition, several S/S ligands were also investigated for the asymmetric hydrogenation of olefins. In 1977, James and McMillan reported the synthesis of various disulfoxide ligands, which were applied to the asymmetric ruthenium-catalysed hydrogenation of prochiral olefinic acid derivatives, such as itaconic acid. These ligands, depicted in Scheme 8.16, were active to provide... 

In 1998, Ruiz et al. reported the synthesis of new chiral dithioether ligands based on a pyrrolidine backbone from (+ )-L-tartaric acid. Their corresponding cationic iridium complexes were further evaluated as catalysts for the asymmetric hydrogenation of prochiral dehydroamino acid derivatives and itaconic acid, providing enantioselectivities of up to 68% ee, as shown in Scheme 8.18. 

Scheme 8.16 Hydrogenation of itaconic acid with disulfoxide ligands.

Enantioselectivities of up to 47% ee were reported by Ruiz et al. in 1997 for the asymmetric hydrogenation of various prochiral dehydroamino acid derivatives and itaconic acid by using iridium cationic complexes of the novel chiral... 

On the other hand, James reported, in 1976, the use of a chiral sulfoxide as a ligand of ruthenium for the asymmetric hydrogenation of itaconic acid, providing a low enantioselectivity of 12% ee (Scheme 8.23). ... 

Hydride-promoted reactions are also well known, such as the acrylic and vinylacrylic syntheses (examples 7-10, Table VII). Some less-known compounds, which form in the presence of halide ions added to tetracar-bonylnickel, have been described by Foa and Cassar (example 11, Table VII). Reaction of allene to form methacrylates, and of propargyl chloride to give itaconic acid (via butadienoic acid), have been reported (examples 13 and 14, Table VII). 1,5-Hexadiene has been shown to be a very good substrate to obtain cyclic ketones in the presence of hydrogen chloride and tetracarbonylnickel (example 15, Table VII). The latter has also been used to form esters from olefins (example 16, Table VII). In the presence of an organic acid branched esters form regioselectivity (193). 

Itaconic acid was hydrogenated rapidly to a 20% ee, and kinetic and spectrophotometric studies on this system were interpreted in terms of a mechanism involving a standard unsaturate route [cf. Eq. (5)]. The actual catalyst was thought to be HRh(DIOP)(DIOP ), where DIOP represents a monodentate DIOP with one dangling —CH2PPh2 moiety (273, 275). Rhodium(I) carbonyls (276) and ruthenium(II) complexes (90, 275) (Section III,B) containing monodentate DIOP have been isolated. 

In the early 1990s, Burk introduced a new series of efficient chiral bisphospholane ligands BPE and DuPhos.55,55a-55c The invention of these ligands has expanded the scope of substrates in Rh-catalyzed enantioselective hydrogenation. For example, with Rh-DuPhos or Rh-BPE as catalysts, extremely high efficiencies have been observed in the asymmetric hydrogenation of a-(acylamino)acrylic acids, enamides, enol acetates, /3-keto esters, unsaturated carboxylic acids, and itaconic acids. 

In contrast to the many successful examples for hydrogenation of the parent itaconic acid or its dimethyl ester, only a few ligands have been reported to be efficient for the hydrogenation of / -substituted itaconic acid derivatives. Rh complexes with chiral ligands such as MOD-DIOP,69,69a 69h BPPM,246 Et-DuPhos,247 and TangPhos116 are... 

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

Knowles reported the hydrogenation of a-phenylacrylic acid and itaconic acid with 15% and 3% optical purity, respectively, by using [RhCl3(P )3] [P = (R)-(-)-methyl-n-propylphenylphosphine] as homogeneous catalyst [38]. Horner found that a-ethylstyrene and a-methoxystyrene can be hydrogenated to (S)-(+)-2-phe-nylbutane (7-8% optical purity) and (R)-(+)-l-methoxy-l-phenylethane (3-4% optical purity), respectively, by using the complex formed in situ from [Rh(l,5-hexadiene)Cl]2 and (S)-(-)-methyl- -propylphenylphosphine as catalyst [39]. 

Scheme 20.18 Reduction of the C-C double bond of itaconic acid (51) utilizing a rhodium catalyst (54) and formic acid (49) as hydrogen donor.

During the 1980s, Achiwa and colleagues examined a number of derivatives of DIOP, and found that MOD-DIOP (12c) allowed for the enantioselective hydrogenation of itaconic acid derivatives with >96% ee [68-75]. 

Several methods have been described to liberate the hydroxyl groups from 24 to produce the water-soluble, tetrahydroxyl bidentate ligand 25 [52, 53b]. Water-soluble ligands are of interest due to the prospect of recycling the catalyst into an aqueous phase, ideally without loss of performance. The enantiomeric hydrogenation of itaconic acid was performed in aqueous methanol over a range of solvent compositions (MeOH H20, 9 1 to 3 97), with consistently excellent levels of performance (100% conversion, 99% ee, SCR 100, 12 h) [52 b]. Interest-... 

The enantioselective hydrogenation of a,fj- or / ,y-unsaturated acid derivatives and ester substrates including itaconic acids, acrylic acid derivatives, buteno-lides, and dehydrojasmonates, is a practical and efficient methodology for accessing, amongst others, chiral acids, chiral a-hydroxy acids, chiral lactones and chiral amides. These are of particular importance across the pharmaceutical and the flavors and fragrances industries. 

Table 24.4 Phospholanes reported to hydrogenate model itaconic acid substrates in >95% ee. Rh-catalyst...

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