Epoxidation, partial

The (partial) description of the synthesis and coupling of the five fragments starts with the cyclohexyl moiety C —C. The first step involved the enantio- and diastereoselective harpless epoxidation of l,4-pentadien-3-ol described on p. 126f. The epoxide was converted in four steps to a d-vinyl d-lactone which gave a 3-cyclohexenecarboxylate via Ireland-CIaisen rearrangement (cf. p. 87). Uncatalysed hydroboration and oxidation (cf. p. 131) yielded the desired trans-2-methoxycyclohexanol which was protected as a silyl ether. The methyl car-... 

Ethylene Oxidation to Ethylene Oxide. A thoroughly investigated reaction catalyzed by a supported metal is the commercially appHed partial oxidation of ethylene to give ethylene oxide (90). The desired reaction is the formation of ethylene oxide, ie, epoxidation the following reaction scheme is a good approximation ... 

Epoxides are normally hydrogenated in preference to saturated ketones but double bonds are usually reduced under these conditions. It is possible in some cases to selectively cleave an epoxide without saturating double bonds by the use of the deactivated catalysts recommended for the partial reduction of acetylenes (see section IV) or by the addition of silver nitrate to the palladium-catalyzed reaction mixture. " ... 

In some cases products of rearrangement are obtained either partially or exclusively on treatment of Grignard reagents with epoxides. Thus, reaction of the 2/ ,3/ -epoxide (14) with methyl Grignard reagent affords a mixture of two epimeric secondary A-nor alcohols (15) in 80% yield and the tertiary hydroxy compound, 2a-methyl-5a-cholestan-2/f-ol (16) in 15 % yield. ... 

A more efficient agent than peroxy compounds for the epoxidation of fluoro-olefins with nonfluonnated double bond is the hypofluorous acid-acetomtrile complex [22] Perfluoroalkylethenes react with this agent at room temperature within 2-3 h with moderate yields (equation 13), whereas olefins with strongly electron-deficient double bond or electron-poor, sterically hindered olefins, for example l,2-bis(perfluorobutyl)ethene and perfluoro-(l-alkylethyl)ethenes, are practically inert [22] Epoxidation of a mixture of 3 perfluoroalkyl-1-propenes at 0 C IS finished after 10 mm in 80% yield [22] The trifluorovinyl group in partially fluorinated dienes is not affected by this agent [22] (equation 13)... 

Polyfluoroalkyl- andperfluoroalkyl-substituted CO and CN multiple bonds as dipolarophiles. Dmzo alkanes are well known to react with carbonyl compounds, usually under very mild conditions, to give oxiranes and ketones The reaction has been interpreted as a nucleophilic attack of the diazo alkane on the carbonyl group to yield diazonium betaines or 1,2,3 oxadiazol 2 ines as reaction intermediates, which generally are too unstable to be isolated Aromatic diazo compounds react readily with partially fluorinated and perfluorinated ketones to give l,3,4-oxadiazol-3-ines m high yield At 25 °C and above, the aryloxa-diazolines lose nitrogen to give epoxides [111]... 

Deoxy-D-jcylo hexose 6-(dihydrogen phosphate) (21) has also been synthesized (2) the reaction sequence makes use of 3-deoxy l 2,5 6-di-O-isopropylidene D-galactofuranose (16), a compound that can be easily prepared from D-glucose (2, 60). The mono-isopropylidene derivative (17) formed by partial hydrolysis of the di-ketal is converted into the 6-tosylate (18) by reaction with one molar equivalent of p-toluenesulfonyl chloride. From this the epoxide (19) is formed by reaction with sodium methoxide. Treatment of the anhydro sugar with an aqueous solution of disodium hydrogen phosphate (26) leads to the 6-phosphate (20)... 

A reiterative application of a two-carbon elongation reaction of a chiral carbonyl compound (Homer-Emmonds reaction), reduction (DIBAL) of the obtained trans unsaturated ester, asymmetric epoxidation (SAE or MCPBA) of the resulting allylic alcohol, and then C-2 regioselective addition of a cuprate (Me2CuLi) to the corresponding chiral epoxy alcohol has been utilized for the construction of the polypropionate-derived chain ]R-CH(Me)CH(OH)CH(Me)-R ], present as a partial structure in important natural products such as polyether, ansamycin, or macro-lide antibiotics [52]. A seminal application of this procedure is offered by Kishi s synthesis of the C19-C26 polyketide-type aliphatic segment of rifamycin S, starting from aldehyde 105 (Scheme 8.29) [53]. 

Epoxidized oils were also used to modify PLA Ali et ah (2009) reported that its use as a plasticizer to improve flexibility. Thermal and scanning electron microscope analysis revealed that epoxidized soybean oil is partially miscible with PLA. Rheological and mechanical properties of PLA/epoxidized soybean oil blends were studied by Xu and Qu (2009) Epoxidized soybean oil exhibited a positive effect on both the elongation at break and melt rheology. Al-Mulla et al. (2010b) also reported that plasticization of PLA (epoxidized palm oil) was carried out via solution casting process using chloroform as a solvent. The results indicated that improved flexibility could be achieved by incorporation of epoxidized palm oil. 

When two polymers interact or react with each other, they are likely to provide a compatible, even a miscible, blend. Epoxidized natural rubber (ENR) interacts with chloro-sulfonated polyethylene (Hypalon) and polyvinyl chloride (PVC) forming partially miscible and miscible blends, respectively, due to the reaction between chlorosulfonic acid group and chlorine with epoxy group of ENR. Chiu et al. have studied the blends of chlorinated polyethylene (CR) with ENR at blend ratios of 75 25, 50 50, and 25 75, as well as pure rubbers using sulfur (Sg), 2-mercapto-benzothiazole, and 2-benzothiazole disulfide as vulcanizing agents [32]. They have studied Mooney viscosity, scorch... 

A complementary approach has been reported very recently [43]. hi this case negative charges were introduced into the salen ligand Iq (Fig. 14) with the aim of exchanging it on cationic supports, such as a layered double (Zn, Al) hydroxide. The expansion in the basal spacing indicated intercalation, at least partially, of the Ig-Mn complex between the layers of [Zn2,i5Alo,86(OH)6,o2]- The complex was used in the epoxidation of (i )-limonene with molecular oxygen and pivalaldehyde. The use of N-... 

The same type of porphyrin-Ru complex was immobilized by coordina-tive adsorption on aminopropylsilicas (Fig. 26) as either amorphous or crystalline supports [79]. Mesoporous crystalline MCM-48 was the best support, as shown by the improved results obtained in the epoxidation of styrene with 2,6-dichloropyridine N-oxide (TON > 13 000 and 74% ee). The versatility of this catalyst was demonstrated in the intramolecular cyclopropanation of frans-cinnamyl diazoacetate. TON was ten times higher than that obtained in solution and 85% ee was observed. The solid was recycled and reused, although partial loss of selectivity occurred. 

Protonatioil of l.he epoxide gives cation (33) which reacts utcr a loose transition state so that a partial posit ve charge appears on the carbon atom under attack. The more stable partial cation is therefore formed. 

The synthesis, structure, and catalytic properties of a Pd11 complex with a partially hydrogenated ligand, shown in Figure 31, are described.393 This study provides the first asymmetric epoxidation of alkenes catalyzed by a palladium complex.393... 

Figure 31 A Pd11 complex with a partially hydrogenated ligand acts as a catalyst for asymmetric epoxidation.

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