Monsanto group

The Monsanto group have used the cationic catalysts Rh(diene)(diphosphine)+ (see Section II,B,1) with diphosphine (22), R,R-bis[(anisole)(phenylphosphine)] ethane (BAPPE), to reduce a-acylami-noacrylic acids in basic alcohol solution to products with 95- 96% ee (244, 245). 

A group at Monsanto has also studied the catalysis of the water-gas shift reaction by rhodium carbonyl iodide (103b). The main difference between their work and our own is the choice of reaction conditions. Their study was conducted at 185°C under 200-400 psig carbon monoxide. Despite this drastic difference in reaction conditions, the studies are surprisingly consistent. In particular, the Monsanto group also finds evidence for two rate-limiting reactions. They did not find this by temperature variation, but instead, consistent with our own work, find that at low acid and iodide... 

From 1978 to 1980, Henis and Tripodi [6,23], then at Monsanto, devised an ingenious solution to the membrane defect problem their approach is illustrated in Figure 8.8. The Monsanto group made Loeb-Sourirajan hollow fiber membranes... 

The first examples of asymmetric hydrogenation based on this principle were reported by Knowles and co-workers (the Monsanto group) in 1968 (12). Rhodium complexes of the type RhL3Cl3 (where L was a chiral phosphine) were used in the hydrogenation of a-phenylacrylic acid (atropic acid) and itaconic acid under the conditions indicated in Fig. 3. When L was (R)-( )-methylphenyl-n-propylphosphine,3 15% optically pure (S)-(+)-a-phenyl-pro-pionic acid and 3% optically pure methylsuccinic acid (configuration unreported) were obtained. 

Although the structure of the active catalyst obtained in solution was uncertain, the Monsanto group suggested at the time that Wilkinson-type Rh(I) complexes might be involved. They did not speculate on how the reduction of Rh(HI) to Rh(I) might be accomplished, but one possibility is... 

The Monsanto group also extended their studies to other substrates (particularly a,/3-unsaturated acids) and other phosphines. In these later experiments, they generated the catalyst in situ, as the Horner group had done. A methanol solution containing an a-substituted acrylic acid and a trace amount of triethyla-mine was then added, and hydrogenations were carried out at 30 atm H2 and 60°C. For various combinations of olefin and chiral ligand, optica] purities ranged from 3 to 21% (Fig. 6). 

As described above, the rhodium-phosphine catalysts used extensively by the Horner and the Monsanto groups contained phosphines that were asymmetric... 

An even more efficient asymmetric synthesis of a-amino acid derivatives has been described by the Monsanto group (20a-e). They have found that chiral o-anisylcyclohexylmethylphosphine (ACMP) (II), like DIOP, exerts an extra-... 

Asymmetric Homogeneous Hydrogenations of ot-Acylaminoacrylic Acids with the Monsanto Group [i+)-(R)-ACMP] Catalysta... 

Two kinds of chiral tertiary phosphine ligands have been used in asymmetric hydrogenation experiments involving rhodium complexes the Horner and Monsanto groups have concentrated on ligands whose chirality is centered at an asymmetric phosphorus atom, and the New Hampshire and Paris groups have focused their attention mainly on phosphides that carry chiral carbon moieties. 

The Monsanto Group has recently reported enantiomeric excesses of 95-96% for the hydrogenation of a-acylaminoacrylic acids using a chiral diphosphine [l,2-di-(0-anisyl-phenylphosphino) ethane] as a ligand (49). The chiral phosphine was prepared by oxidative coupling of chiral o-anisylmethylphenylphosphine oxide (50), followed by deoxygenation with trichlorosilane and tri-n-butylamine in acetonitrile. 

L-dopa has one chiral center. Until the 1970s, only enzymes could produce chiral molecules. In the 1970s, workers at Monsanto developed the first nonbiological cataly.st for the synthesis of chiral molecules. The Monsanto group shnv etl tluit catalj sis of the type ... 

However, the monofluoro analog 12 has been made the enzyme itself will assemble it fiom Z-fluoro-PEP and S-3-P, as Mark Walker and the Monsanto group have recently shown (Figure 9).3 Actually, EPSP synthase induces formation of 12, it doesn t catalyze it This analog is a powerful inhibitor and the enzyme can t carry it further to fluoro-EPSP thus, turnover and true catalysis do not occur. We have tried to get to this monofluoro derivative fiom the other direction, namely from Z-fluoro-EPSP, but the enzyme will not oblige us. Enzymatic formation of 12 from S-3-P and Z-fluoro-PEP takes less than a minute, but even weeks of incubation of enzyme, phosphate, and Z-fluoro-EPSP give no evidence for formation of 12 or Z-fluoro-PEP.37... 

The invention of another type of ligand by Monsanto group was R,R-PPh(2-PhOCH3)CH2CH2PPh(2-PhOCH3) (DIPAM) and its use as thodium complex in asy-mmetric hydrogenation for production of L-DOPA, has improved the yield (> 95 %). 

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