Jacobsen system

A. Hensten, N. Jacobsen, Systemic toxicity and hypersensitivity. Biomaterials Science An Introduction to Materials in Medicine, third ed., Academic Press, Elsevier, Waltham, MA, USA, 2013. 

Lynch and co-workers from the Merck Research Laboratories made elegant use of the Jacobsen system in their synthesis of CDP840 (Scheme 14.53). Epoxidation of tri-substituted alkene 134 with catalyst 135 furnished 136 in 89% ee and 58% yield. The stereo-outcome is dictated by formation of the lower energy Z-olefin intermediate. Epoxide 136 was further elaborated to secondary alcohol 137 in a particularly unusual gin-selective reduction of the epoxide with LiBH4, under the influence of Lewis acidic reductant borane. While the mechanism of this reduction is unknown, it may be due to carbocation formation at the doubly benzylic centre, followed by internal delivery of hydride directed by the in situ generated alkoxide. 

During the early development of the Jacobsen-Katsuki epoxidation reaetion, it was elear that trans-disubstituted olefins were very poor substrates (slow reaetion rates, low enantioseleetivity) eompared to cis-disubstituted olefins. The side-on approaeh model originally proposed by Groves for porphyrin epoxidation systems was used to rationalize the differenees observed in the epoxidation of the cis and trans-disubstituted elasses (Seheme 1.4.7). ... 

Chiral salen chromium and cobalt complexes have been shown by Jacobsen et al. to catalyze an enantioselective cycloaddition reaction of carbonyl compounds with dienes [22]. The cycloaddition reaction of different aldehydes 1 containing aromatic, aliphatic, and conjugated substituents with Danishefsky s diene 2a catalyzed by the chiral salen-chromium(III) complexes 14a,b proceeds in up to 98% yield and with moderate to high ee (Scheme 4.14). It was found that the presence of oven-dried powdered 4 A molecular sieves led to increased yield and enantioselectivity. The lowest ee (62% ee, catalyst 14b) was obtained for hexanal and the highest (93% ee, catalyst 14a) was obtained for cyclohexyl aldehyde. The mechanism of the cycloaddition reaction was investigated in terms of a traditional cycloaddition, or formation of the cycloaddition product via a Mukaiyama aldol-reaction path. In the presence of the chiral salen-chromium(III) catalyst system NMR spectroscopy of the crude reaction mixture of the reaction of benzaldehyde with Danishefsky s diene revealed the exclusive presence of the cycloaddition-pathway product. The Mukaiyama aldol condensation product was prepared independently and subjected to the conditions of the chiral salen-chromium(III)-catalyzed reactions. No detectable cycloaddition product could be observed. These results point towards a [2-i-4]-cydoaddition mechanism. 

Jacobsen subsequently reported a practical and efficient method for promoting the highly enantioselective addition of TMSN3 to meso-epoxides (Scheme 7.3) [4]. The chiral (salen)Cl-Cl catalyst 2 is available commercially and is bench-stable. Other practical advantages of the system include the mild reaction conditions, tolerance of some Lewis basic functional groups, catalyst recyclability (up to 10 times at 1 mol% with no loss in activity or enantioselectivity), and amenability to use under solvent-free conditions. Song later demonstrated that the reaction could be performed in room temperature ionic liquids, such as l-butyl-3-methylimidazo-lium salts. Extraction of the product mixture with hexane allowed catalyst recycling and product isolation without recourse to distillation (Scheme 7.4) [5]. 

Jacobsen demonstrated that the (salen)Cr system used to effect intermolecular, cooperative asymmetric azidolysis of meso-epoxides (Schemes 7.3 and 7.5) could be applied to sulfur-centered nucleophiles (Scheme 7.13). In order to overcome moderate enantioselectivity (<60% ee), a dithiol nucleophile was employed as part of a double resolution strategy in which the minor enantiomer of the monoaddition product reacts preferentially to form the meso- bis-addition product, thereby increasing the ee of the C2-symmetric bis-addition product. Enantiopure 1,2-mer-capto alcohols (>99% ee) were obtained from the meso-epoxide in ca. 50% overall yield by a burdensome (though effective) multistep sequence, [23]. 

Fueled by the success of the Mn (salen) catalysts, new forays have been launched into the realm of hybrid catalyst systems. For example, the Mn-picolinamide-salicylidene complexes (i.e., 13) represent novel oxidation-resistant catalysts which exhibit higher turnover rates than the corresponding Jacobsen-type catalysts. These hybrids are particularly well-suited to the low-cost-but relatively aggressive-oxidant systems, such as bleach. In fact, the epoxidation of trans-P-methylstyrene (14) in the presence of 5 mol% of catalyst 13 and an excess of sodium hypochlorite proceeds with an ee of 53%. Understanding of the mechanistic aspects of these catalysts is complicated by their lack of C2 symmetry. For example, it is not yet clear whether the 5-membered or 6-membered metallocycle plays the decisive role in enantioselectivity however, in any event, the active form is believed to be a manganese 0x0 complex <96TL2725>. 

The limitations of the system with regard to substrates and oxidants was attributed to the strong electron-withdrawing character of the perfluorinated chains and the lower steric hindrance in the position adjacent to phenols, in marked contrast to the ferf-butyl groups present in Jacobsen s catalyst, hi view of this, a second generation of fluorinated salen ligands le and If was... 

Study [23] Jacobsen s complex was entrapped in the final step of the zeohte synthesis (method C). This process was possible because MCM-22 zeohte is prepared by condensation of a layered precursor, which is exchangeable by the catalytic complex. Leaching of Mn was not observed in these systems, which is not unexpected bearing in mind that the complex is also bovmd to the zeolite structure through an electrostatic interaction. 

Oehme G (1999) Catalyst immobilization two-phase systems. In Jacobsen EN, Pfaltz A, Yamamoto H (eds) Comprehensive asymmetric catalysis, vol III. Springer, Berlin Heidelberg New York, p 1377... 

The Cu/ZnO system is very dynamic. The morphology of the Cu particles responds immediately to a change in reduction potential of the gas mixture above it. EXAFS studies suggest that the change in morphology is associated vith the extent that the metal particles vet the underlying support [B.S. Clausen, J. Schiotz, L. Gr4-bffik, C.V. Ovesen, K.W. Jacobsen, J.K. Norskov and H. Topsoe, Top. Catal. 1 (1994)... 

Braughler, M.J., Hall, E.D., Jacobsen, E.J., McCall, J.M. and Means, E.D. (1989). The 21-aminosteroids potent inhibitors of lipid peroxidation for the treatment of central nervous system trauma and ischemia. Drugs Future 14, 143-152. 

Electrospray Ionization - Mass Spectrometry (ESI-MS). The Jacobsen s Co-salen catalysts dissolved in dichloromethane were pumped to the mass spectrometer system after dilution with methanol at a flow rate of 50 pi min and 600 scans were collected in 1 min. 

The synthesis of the first polymer-supported chiral Mn-salen derivatives was reported independently by Sivaram171 and Minutolo.171-173 Different monomeric Jacobsen-type units, containing two polymerizable vinyl groups, were copolymerized with styrene and divinylbenzene to yield the corresponding cross-linked polymers as a monolithic compact block.174-176 The less mobile system (Figure 19) with no spacer between the aromatic ring and the polymer backbone is less enantioselective. 

Flynn G. J., Keller F. P., Feser M., Wirick S. and Jacobsen C. (2003). The origin of organic matter in the solar system evidence from the interplanetary dust particles. Geochimica et Cosmochimica Acta 67 4791. 

Based on these criteria, the following fractions are found to be relevant in the case of heterotrophic wastewater processes in sewer systems (Hvitved-Jacobsen et al., 1998, 1999) ... 

Nielsen, P.H., K. Raunkjaer, N.H. Norsker, N.Aa. Jensen, and T. Hvitved-Jacobsen (1992), Transformation of wastewater in sewer systems —Areview, Water Sci. Tech., 25(6), 17-31. Norsker, N.-H., P.H. Nielsen, and T. Hvitved-Jacobsen (1995), Influence of oxygen on biofilm growth and potential sulfate reduction in gravity sewer biofilm, Water Sci. Tech., 31(7),... 

The existence of different fractions of particulate substrates in terms of then-specific hydrolysis rates is an important finding that originates from investigations of wastewater and resuspended sediments (Bjerre et al 1995 Bjerre et al., 1998a Vollertsen and Hvitved-Jacobsen, 1998 Tanaka and Hvitved-Jacobsen, 1998a). Typically, two to three fractions must be considered to interpret the hydrolysis when it occurs in wastewater of sewer systems (cf. Section 3.2.6). 

Vollertsen, J. and T. Hvitved-Jacobsen (1999), Stoichiometric and kinetic model parameters for microbial transformations of suspended solids in combined sewer systems, Water Res., 33(14), 3127-3141. 

Tanaka, N., T. Hvitved-Jacobsen, and T. Horie (2000a), Transformations of carbon and sulfur wastewater components under aerobic-anaerobic transient conditions in sewer systems, Water Env. Res., 72(6), 651-664. 

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