Epoxides Sharpless oxidation

SAE reaction see Sharpless asymmetric epoxidation Saegusa oxidation 390 samarium diiodide 496, 633, 638 saponification 49, 207 sativene 382 f. 

This method has proven to be an extremely useful means of synthesizing enantiomerically enriched compounds. Various improvements in the methods for carrying out the Sharpless oxidation have been developed.48 The reaction can be done with catalytic amounts of titanium isopropoxide and the tartrate ester.49 This procedure uses molecular sieves to sequester water, which has a deleterious effect on both the rate and enantioselectivity of the reaction. Scheme 12.9 gives some examples of enantioselective epoxidation of allylic alcohols. 

Earlier on in our work, we also used the other legendary Sharpless oxidation, the asymmetric epoxidation [22] for the transformation of the allylic alcohol 17 into the epoxide 18. In the presence of (+)-diethyl tartrate, 17 was converted... 

We (J. Org. Chem. 2004,69, 7234) used the power of the Sharpless oxidations to convert the prochiral 10 into the epoxy diol 11. Base-catalyzed cascade cyclization then converted 11 into crystalline 12, again with high diastereomeric and enantiomeric purity. An advantage of this approach is that by changing the absolute sense of the epoxidation and/or the dihydroxylation, it should be possible to selectively prepare each of the four enantiomerically-pure diastereomers of 12. 

The asymmetric oxidation of sulphides to chiral sulphoxides with t-butyl hydroperoxide is catalysed very effectively by a titanium complex, produced in situ from a titanium alkoxide and a chiral binaphthol, with enantioselectivities up to 96%342. The Sharpless oxidation of aryl cinnamyl selenides 217 gave a chiral 1-phenyl-2-propen-l-ol (218) via an asymmetric [2,3] sigmatropic shift (Scheme 4)343. For other titanium-catalysed epoxidations, see Section V.D.l on vanadium catalysis. 

Epoxy alcohols (A in Figure 17.43) are accessible in enantiomerically pure form via the Sharpless oxidation (Figure 3.35). The epoxide substructure of these compounds can be reduced to obtain an alcohol in a regiocontrolled fashion to afford an enantiomerically pure 1,3-diol, B, or an enantiomerically pure 1,2-diol, C (Figure 17.43). The 1,3-diols B and the 1,2-diols C are best accessible via reduction of A with Red-Al [NaAlH2(OCH2CH2 OCH3)2] or DIBAL, respectively. 

Sharpless oxidation of the oxazole 52 provides an intermediate epoxide, which is attacked by the neighboring amino group, eventually leading to the pyrrolo[2,3-r/ isoxazole 53 (Equation 12). Variation of the aryl substituent provided access to a set of related derivatives in excellent yields <2006TL4957>. 

Intramolecular ene reaction,3 A key step in a new route to anthracyclinones such as y-citromycinone (4) is a regioselective intramolecular ene reaction of the unsaturated aldehyde 1 to give 2 in 93% yield. Sharpless oxidation [(CH3)3COOH, VO(acac)2] of 2 is regioselective, giving the desired epoxide 3 as the only isomer. Synthesis of 4 is... 

The conversion of alkenes into epoxides is important not only because it is one of the most reliable routes leading from oxidation level 1 to level 2, but also because reactions of non-symmetrical epoxides with nucleophiles invariably proceed as an attack at the less substituted carbon with inversion of configuration. Thus, hydride reduction of epoxides represents an additional option for the preparation of alcohols (Scheme 2.62), especially valuable for the synthesis of optically pure isomers from epoxides obtained by the Sharpless oxidation. It is also of merit that as a result of alkene-epoxide conversion, a nucleophilic moiety (double bond) is transformed into an electrophilic epoxy ring. The latter... 

Ti(OPr )4/Bu OOH/tartrate ester (Sharpless oxidation) (titanium isopropoxide/t-butyl hydroperoxide dialkyl tartrate) Dichloromethane -20 enantioselective epoxidation of allylic alcohols... 

Related reactions Jacobsen-Katsuki epoxidation, Prilezhaev oxidation, Rubottom oxidation, Sharpless asymmetric epoxidation, Shi... 

Key Words Ethylene oxide, Propylene oxide. Epoxybutene, Market, Isoamylene oxide. Cyclohexene oxide. Styrene oxide, Norbornene oxide. Epichlorohydrin, Epoxy resins, Carbamazepine, Terpenes, Limonene, a-Pinene, Fatty acid epoxides, Allyl epoxides, Sharpless epoxidation. Turnover frequency, Space time yield. Hydrogen peroxide, Polyoxometallates, Phase-transfer reagents, Methyltrioxorhenium (MTO), Fluorinated acetone, Alkylmetaborate esters. Alumina, Iminium salts, Porphyrins, Jacobsen-Katsuki oxidation, Salen, Peroxoacetic acid, P450 BM-3, Escherichia coli, lodosylbenzene, Oxometallacycle, DFT, Lewis acid mechanism, Metalladioxolane, Mimoun complex, Sheldon complex, Michaelis-Menten, Schiff bases. Redox mechanism. Oxygen-rebound mechanism, Spiro structure. 2008 Elsevier B.V. 

Sharpless oxidation, epoxidation Ti/ROOH/tartrate May Baker, Upjohn, ARCO, 1981... 

The key intermediate 79 was demonstrated for the synthesis of maysine as illustrated in Scheme 10. This compound 79 was reduced to the alcohol 80 and the olefin C4 5 was epoxidized with f-butylhydroperoxide and Ti(IV) catalyst (without any chiral auxiliary) to yield selectively the P-epoxide 81. Oxidation with MCPBA, on the other hand, selectively provided a-epoxide 82. These selectivities were found to be due to substrate control but not to reagent control. Sharpless condition with chiral auxiliary in this case showed substrate... 

Allylic alcohols are converted to epoxides by oxidation with tert-hutyl hydroperoxide in the presence of certain transition metals. The most significant aspect of this reaction— called the Sharpless epoxidation— is its high enantioselectivity when carried out using a combination of tert-hutyl hydroperoxide, titanium(IV) isopropoxide, and diethyl tartrate. 

In contrast to the developments in the areas of arene oxidation, a general method for the controlled epoxidation of alkenes has not been found. There have been reports that indicate that terminal alkenes can be converted into optically active epoxides, but there is nothing yet to rival the Sharpless oxidation of allylic alcohols using a chiral titanium catalyst (Scheme 4.27) as a general synthetic method. However, it should be... 

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