Kinetic resolution of epoxides

Another application of salen ligands is the hydrolytic kinetic resolution of epoxides (Scheme 3). For this purpose cobalt complexes are efficient, and fiu-... 

Scheme 20. Jacobsen s sequential use of catalytic asymmetric reactions, including his Cr-catalyzed kinetic resolution of epoxides in the total synthesis of taurospongin A (1998).

ARO reaction with phenols and alcohols as nucleophiles is a logical extension of HKR of epoxides to synthesize libraries of stereochemically defined ring-opened products in high optical purity. To this effect Annis and Jacobsen [69] used their polymer-supported Co(salen) complex 36 as catalyst for kinetic resolution of epoxides with phenols to give l-aiyloxy-2-alcohols in high yield, purity and ee (Scheme 17). Conducting the same reaction in the presence of tris(trifluoromethyl)methanol, a volatile, nonnucleophilic protic acid additive accelerates KR reaction with no compromise with enantioselectivity and yield. Presumably the additive helped in maintaining the Co(III) oxidation state of the catalyst. 

Welbes, L. L. Searrow, R. C. Borovik, A. S. (2004) Development of porous materials for heterogeneous eatalysis Kinetic resolution of epoxides, Chem. Commun., 2544-2545. 

Choi, S. D. Kim, G. J. (2004) Enantioseleetive hydrolytie kinetic resolution of epoxides eatalyzed by chiral Co(III) salen eomplexes immobilized in the membrane reaetor., Catal. Lett., 92 35-40. 

Heterogenization of homogeneous metal complex catalysts represents one way to improve the total turnover number for expensive or toxic catalysts. Two case studies in catalyst immobilization are presented here. Immobilization of Pd(II) SCS and PCP pincer complexes for use in Heck coupling reactions does not lead to stable, recyclable catalysts, as all catalysis is shown to be associated with leached palladium species. In contrast, when immobilizing Co(II) salen complexes for kinetic resolutions of epoxides, immobilization can lead to enhanced catalytic properties, including improved reaction rates while still obtaining excellent enantioselectivity and catalyst recyclability. 

Epoxide hydrolase Kinetic resolution of epoxides in Tris buffer/ octane [18]... 

Enantioselective Epoxidation, Ring-Opening and Kinetic Resolution of Epoxides... 

Choi SD and Kim GJ. Enantioselective hydrolytic kinetic resolution of epoxides catalyzed by chiral Co(III) salten complexes immobilised in the membrane reactor. Catal Lett 2004 92(l-2) 35M-0. 

MTO [methyltrioxorhenium(VII), cf. Chapter 3.3.13] can be used as a catalyst for the epoxidation of olefins with urea hydroperoxide in [EMIMJBF4 [19]. The activity is reported to be comparable with the reaction in organic solvents but side reactions are suppressed. The use of an ionic liquid as a co-solvent in CH2CI2 for the enantioselective Mn-salen complex-catalyzed epoxidation of olefins with Na(OCl) was reported to result in enhanced reaction rates at no loss of enantioselectivity [20]. Cr-salen complexes can further be used for the asymmetric kinetic resolution of epoxides by ring-opening with azide [21]. 

TONs up to 9000 [11c]. Of potential interest is the use of ionic liquids which allow recycling of the catalyst (cf. Section 3.1.1.2.2) [33]. SALEN complexes are also eminently suitable for the kinetic resolution of epoxides [12 u] especially promising for commercial applications is hydrolytic ring-opening using Co/ SALEN complexes [34] (42 5). a,jff-Unsaturated ketones can be epoxidized with hydrogen peroxide in presence of a polypeptide catalyst with ee values up to >98% [35]. 

Liu, Y., Dimare, M., Marchese, S. A., Jacobsen, E. N., Jasmin, S. Hydrolytic kinetic resolution of epoxides using chiral cobalt catalysts. WO 2002-US26729 (2003018520), 2003 (Rhodia/Chirex, Inc., USA). 47 pp... 

The kinetic resolution of epoxide-bearing substrates has also been achieved... 

The kinetic resolution of epoxide-bearing substrates has also been achieved via a biotransformation different from hydrolysis. Thus, Weijer et al. [141]... 

Cr Vsalen) complexes arc widely employed as catalysts of stereoselective alkene epoxidations [3,85,33,15.86], kinetic resolution of epoxides [87-89], alcohol oxidations [90],... 

The attempt to immobilize a perfluoro-tagged Co(III) salen complex 40 (Fig. 19) on FRPSG did not lead to active catalysts [71]. While complex 40 was active in solution as catalyst for the hydrolytic kinetic resolution of epoxides, the adsorbed complex was inactive. The authors attributed this to site-isolation on the solid support, which counteracts the proposed cooperative reaction mechanism [72,73]. 

Jacobsen and Ready <0IJA2687> have reported on the development of a highly aetive cyclic oligosalen catalyst (66), which is remarkably effective in promoting the asymmetric ring opening of epoxides by water and alcohols. For example, exposure of the notoriously recalcitrant substrate cyclohexene oxide (67) to water in methylene chloride/acetonitrile and 1.5 mol% of catalyst 66 led to smooth conversion to the chiral diol 68 in 98% yield and 94% ee. This catalyst is also effective in the kinetic resolution of epoxides with alcohols (i.e., 69 71)<01JA2687>. 

This reaction has been extended to occur in ionic liquidj and used for the highly selective hydrolytic kinetic resolution of epoxides. ... 

Hydrolytic kinetic resolution of epoxides Dihydroxylation of C=C Hydroformylation of C=C Hydrosilylation and hydroboration ofC=C... 

Jacobsen s hydrolytic kinetic resolution of epoxides catalyzed by a Co(salen) catalyst analogous to the one used for asymmetric epoxidation has brought a considerable advance to the use of epoxides. Indeed, these substrates are among the most useful reagents in organic synthesis. One of the two epoxide enantiomers is selectively opened by a nucleophile (including water), which leads to both the terminal epoxide and the functional alcohol in quantitative yields (i.e. 50% of each) and more than 98 e.e. for both products. This system has been applied industrially by Rhodia on ton-scales for hydrolysis of propylene oxide and epichlorhydrin. - ... 

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