Enantioselective epoxidation of olefins

A chiral diphosphine ligand was bound to silica via carbamate links and was used for enantioselective hydrogenation.178 The activity of the neutral catalyst decreased when the loading was increased. It clearly indicates the formation of catalytically inactive chlorine-bridged dimers. At the same time, the cationic diphosphine-Rh catalysts had no tendency to interact with each other (site isolation).179 New cross-linked chiral transition-metal-complexing polymers were used for the chemo- and enantioselective epoxidation of olefins.180... 

The enantioselective epoxidation of olefins has received much attention since the corresponding chiral epoxides have become important building units for the... 

ENANTIOSELECTIVE epoxidation of OLEFINS USING PHASE TRANSFER CONDITIONS AND... 

ENANTIOSELECTIVE EPOXIDATION OF OLEFINS USING PHASE TRANSFER CONDITIONS AND A CHIRAL [AZEPINIUM][TRISPHAT] SALT AS CATALYST... 

Table 6.11 Enantioselective epoxidation of olefins 1 to 5 in the presence of [6-N-((S)-3,3-dimethylbutan-2-yl)-5/f-dibenz[c,e]azepinium][rac-TRISPHAT] as catalyst."...

Rose E, Andrioletti B, Zrig S, Quelquejeu-Etheve, M. Enantioselective epoxidation of olefins with chiral metalloporphyrin catalysts. Chem. Soc. Rev. 2005 34 573-583. 

The use of fluorous chiral manganese salene (Jacobsen-Katsuki) catalysts (29, 30) [30] in combination with different oxidants enables enantioselective epoxidation of olefins [31] in high yields and with moderate to high enantiomeric excess (Scheme 3.12). 

Scheme 3.12 Enantioselective epoxidation of olefins /ith fluorous Jacobsen-Katsuki catalysts 29 and 30 (obove) [31a], and the synthesis of these catalysts (below) (D-100 consists mainly of n-perfluorooctane, b. p. 100°C, and is commercially available from Ausimont).

Gross et al. reported the first use of a chiral ruthenium porphyrin Ru"(L,)(CO) as a catalyst for styrene epoxidation . Chiral ruthenium porphyrin systems have also been reported by Che et a/. . The utilization of another chiral ruthenium porphyrin, Ru"(L2)(CO) as a catalyst for enantioselective epoxidation of olefins with 2,6-dichloropyridine A-oxide has been described by Berkessel and Frauenkron ". The highest enantiomeric excesses of the oxiranes were obtained in the epoxidation of tetrahydronaphthalene and styrene, 77% and 70% ee, respectively, with high jdelds (up to 88%). Terminal aliphatic olefins and tra 5-disubstituted olefins, represented by 1-octene and rraw-stilbene, were sluggish substrates and gave low ee s. The epoxidation of tetrahydronaphthalene with iodosylbenzene catalyzed by Ru(II)(L2)(CO) produced only 52% ee... 

Enantioselective Epoxidation of Olefins with Hydrogen Peroxide with CA[Mn]. 54... 

In 2006, two groups reported the enantioselective epoxidation of olefins by manganese-substituted carbonic anhydrase [38, 46]. In the presence of bicarbonate, hydrogen peroxide, and BBS buffer, CA[Mn] also catalyzed the enantioselective... 

Because of this catalyst degradation, organometallic catalysts are currently the best synthetic reagents for enantioselective epoxidation of olefins. Chiral Mn(III)-salen complexes yield up to 99% ee for cw-disubstituted, tri- and tetra-substituted alkenes [62], but the best results require less desirable oxidants - iodosyl benzene or hypochlorite. Other catalysts accept a more limited substrate range the Sharpless-Katsuki titanium-tartrate ester [65] for allylic alcohols and the JuUa-Colonna epoxidation for a,P-unsaturated ketones [66]. 

Dinuclear Mn(IV) catalysts were successfully applied for the epoxidation of 4-benzoic acid and styrene in aqueous systems [18], for the epoxidation of styrene and dodecene in two-phase systems [19g] as weU as in methanol and acetone [17d, 19b,g,h], and for the epoxidation of olefins in acetonitrile [19i], aqueous acetonitrile [17f, 19c], acetone [17d, 19b,h], methanol [19i], and acetone-methanol-water mixtures [19j]. Enantioselective epoxidations of olefins have been reported for chiral triazacyclononane derivatives boimd to Mn(OAc2) 4 (H2O) in methanol [19k], Heterogenization of the Mn catalysts on silica for the epoxidation of styrene and cyclohexene, on zeolites for olefin epoxidation, and on a solid MnS04 H2O also for olefin epoxidation [20] has also been described. A polymeric structure bearing a dense arrangement of 1,4,7-triazacyclononane moieties can be synthesized by... 

Enantioselective epoxidation of olefins with chiral metaUoporphyrin catalysts 05CSR573. 

Among the major initial impacts of homogeneous catalysis more than 30 years ago was the industrial production of acetaldehyde by the oxidation of ethylene. More recently, enantioselective epoxidation of olefins has been attracting increasing attention in the synthesis of pharmaceutical and specialty chemicals. 

Enantioselective epoxidation of olefins is unique in that it creates two stereogenic centers. The catalyst is prepared quite easily by treating a titanium ( + 4) alkoxide with an (/ )- or (5)-diethyl tartrate (Gao et al., 1987). The peroxidation agent is usually t-butyl hydroperoxide. 

Table 11.1 Enantioselective epoxidation of olefins, at 0°C, catalysed by [Mn (saZew)Cl] complex in homogeneous and heterogeneous phase. ...

Fig. 8. Structure of a Schiffs base complex for enantioselective epoxidation of olefins.

Introduction of bulky and chiral substituents at the 5,10,15,20 (meso)-positions of the porphyrin ring allows for aerobic, enantioselective epoxidation of olefins. Use of chiral Fe(III)- and especially Mn(ni)-... 

GR Haas, JW Kolis. Enantioselective epoxidation of olefins in supercritical carbon dioxide. Proceedings of the 217th ACS National Meeting. Anaheim, CA, 1999. GR Haas, JW Kolis. Oxidation of aUcenes in supercritical carbon dioxide catalyzed by molybdenum hexacarbonyl. Organometallics 17 4454-4460, 1998. 

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