Jacobsen’s catalysts

Conjugated dienes can be epoxidized to provide vinylepoxides. Cyclic substrates react with Katsuki s catalyst to give vinylepoxides with high ees and moderate yields [17], whereas Jacobsen s catalyst gives good yields but moderate enantiose-lectivities [18]. Acyclic substrates were found to isomerize upon epoxidation (Z, )-conjugated dienes reacted selectively at the (Z)-alkene to give trans-vinylepoxides (Scheme 9.4a) [19]. This feature was utilized in the formal synthesis of leuko-triene A4 methyl ester (Scheme 9.4b) [19]. 

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... 

Chiral and achiral Jacobsen s catalysts exhibit similar diatereomeric excesses during the diastereoselective epoxidation of R-(+)-limonene using in situ prepared oxidizing agents. Therefore, the chiral center of the substrate appears to govern the chiral induction. In contrast, the chirality of the Jacobsen s catalyst appears to be responsible for the chiral induction when commercially available oxidants were used. 

Furthermore, the chemical stmcture of the Jacobsen s catalyst is stable in the presence of DMD as oxidant. 

A 100 mL flask was filled with Jacobsen s catalyst (26 mg), (Z)-methyl styrene (lmmol) and dichloromethane (1 mL). The solution was cooled with an ice-bath. To this solution was added the cold solution of bleach previously prepared (3.5 mL). 

A 100 mL flask, was filled with (Z)-ethyl cinnamate, (666 mg of the mixture containing 75 % of (Z)-ethyl cinnamate), 4-phenylpyridine N-oxide (116 mg) and dichloromethane (6mL). Jacobsen s catalyst (108 mg) was then added. 

Chiral irara-cyclohexane- 1,2-diamine was used as the bridging diamine and this led to a successful catalyst [14], often referred to as Jacobsen s catalyst (Figure 14.12). The oxidising agent is household bleach ( ) diluted and buffered... 

Figure 14.20. Jacobsen s catalyst in enantioselective ring opening of epoxide...

To overcome this issue Kureshy et al. [55, 56] reported dimeric form of Jacobsen s catalysts 3, 4. They used the concept of solubility modification by altering the molecular weight of the catalyst so that in a post catalytic work-up procedure the catalyst is precipitated, filtered and used for subsequent catalytic runs. The complexes 3, 4 (0.2 mol % of Co(lll)-salen unit) (Figure 2) were effectively used for HKR of racemic epoxides, e.g., styrene oxide, epichlorohydrin, 1,2-epoxypropane, 1,2-epoxyhexane, 1,2-epoxyoctane, and 1,2-epoxydodecane to achieve corresponding epoxides and 1,2-diols in high optical purity and isolated yields. In this process, once the catalytic reaction is complete the product epoxides were collected by reduced pressure distillation. Addition of diethylether to the residue precipitated the catalyst which was removed by filtration. However, the recovered catalyst was required to be reactivated by its treatment with acetic acid in air. The catalysts were reused 4 times with complete retention of its performance. 

In 1996, Hamann and Hoft were able to obtain 1,2,3,4-tetrahydronaphthyl hydroperoxide (THPO, 16b) in enantiomerically enriched form starting from the racemic mixture by selective decomposition of one enantiomer in the presence of Jacobsen s catalyst 21 . Besides the enantiomerically enriched hydroperoxide (5)-16b, also the corresponding alcohol (/f)-l-tetralol (19b) was isolated in enantiomerically enriched form (opposite... 

SCHEME 155. Oxidation of hydroxylamines to nitrones and a secondary amine to an imine employing Jacobsen s catalyst... 

Heterogeneous Asymmetric Epoxidation of Olefins over Jacobsen s Catalyst Immobilized in Inorganic Porous Materials... 

Fig. 2.1.6.5 (R,R)-(-)-N,N -bis(3,5-di-t-butylsalicylidene)-l,2-cyclohexanediamine metal chloride (Jacobsen s catalyst).

In the present work, the Jacobsen s catalyst was immobilized inside highly dealuminated zeolites X and Y, containing mesopores completely surrounded by micropores, and in Al-MCM-41 via ion exchange. Moreover, the complex was immobilized on modified silica MCM-41 via the metal center and through the salen ligand, respectively. cis-Ethyl cinnamate, (-)-a-pinene, styrene, and 1,2-dihydronaphtalene were used as test molecules for asymmetric epoxidation with NaOCl, m-CPBA (m-chloroperoxybenzoic acid), and dimethyldioxirane (DMD) generated in situ as the oxygen sources. 

Different immobilization methods were applied for Jacobsen s catalyst. The entrapment of the organometallic complex in the supercages of the dealuminated zeolite was achieved without noticeable loss of activity and selectivity. The immobilized catalysts were reusable and did not leach. For the oxidation of (-)-a-pinene the system used only O2 at RT instead of sodium hypochloride at 0 °C. There was a disadvantage in the use of pivalic aldehyde for oxygen transformation via the corresponding peracid. This results in the formation of pivalic acid, which has to be separated from the reaction mixture. 

The number in parentheses stands for the face selectivity. Face selectivity = ee, ram x %trans + eeris x %cis (reference 44). Avith modified Jacobsen s catalyst 12b (4°C) Chang, S. Heid, R.M. Jacobsen, E.N. Tetrahedron Lett., 1994, 35, 669., fWith complex 13. 

Many other projects in the past dealt with the immobilization of the famous chelating salen ligand or salen metal complexes, respectively—the Mnm salen Schiff base complex is also known as Jacobsen s catalyst, and it is used, among others, in asymmetric epoxidation of olefinstttt—mainly onto the surface of MCM-41 and SBA-15. 

Table 3 Results of Diels-Alder reaction between Danishefsky s diene and benzaldehyde catalyzed by 18, 19, and 20 and their comparison with Jacobsen s catalyst 14-Cr/Cl...

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