Hydroxy ethers, oxidation

Chiral acetals/ketals derived from either (R,R)- or (5,5 )-pentanediol have been shown to offer considerable advantages in the synthesis of secondary alcohols with high enantiomeric purity. The reaction of these acetals with a wide variety of carbon nucleophiles in the presence of a Lewis acid results in a highly diastereoselective cleavage of the acetal C-0 bond to give a /1-hydroxy ether, and the desired alcohols can then be obtained by subsequent degradation through simple oxidation elimination. Scheme 2-39 is an example in which H is used as a nucleophile.97... 

Oxidation of silyl enol ethers. Oxidation of silyl enol ethers to a-hydroxy aldehydes or ketones is usually effected with w-chloroperbenzoic acid (6, 112). This oxidation can also be effected by epoxidation with 2-(phenylsulfonyl)-3-( p-nitrophenyl) oxaziridine in CHC1, at 25-60° followed by rearrangement to a-silyloxy carbonyl compounds, which are hydrolyzed to the a-hydroxy carbonyl compound (BujNF or H,0 + ). Yields are moderate to high. Oxidation with a chiral 2-arene-sulfonyloxaziridine shows only modest enantioselectivity. 

Cyclic acetals. In combination with iodine, this reagent resembles lead tetraacetate in the ability to generate alkoxy or aminyl radicals (12,243) under thermal or light activation. This radical oxidation can be used to convert p- or y-hydroxy ethers into dioxolanes or dioxanes.4... 

The results from our work on the reaction of propylene oxide with cobalt carbonyl and base in methanol are given in Table VIII. Several base/metal oxide combinations were evaluated under mild reaction conditions. The difference in activity between the bases was not as pronounced as that observed in the reaction with benzyl halides with the exception of potassium methoxide which, when used alone, gave exclusively the hydroxy ether resulting from methoxide addition to the epoxide ring. However, the activity of sodium... 

In the case of nonsymmetrical epoxides, the regioselectivity is determined by the particular reaction conditions. Thus, styrene oxide (6) undergoes methanolysis in the presence of the Lewis acid catalyst copper(II) tetrafluoroborate to give the hydroxy ether 60, derived from attack of the nucleophile at the more substituted oxiranyl carbon. Similar outcomes have been observed in the solvolysis of 6 with the assistance of aminopropyl silica gel (APSG) supported iodine in catalytic quantities <02SL1251>. This selectivity appears to be much less decisive, however, in the case of monoalkyl epoxides, as illustrated in the corresponding reaction of 1-octene oxide (61), which yields an almost 1 1-mixture of isomers under the same conditions <02OL2817>. 

As well as the above quoted studies this method has also been used to study the interaction between poly(vinylidene fluoride) and poly(methyl methacrylate) , between poly(ethylene oxide) and the hydroxy ether of bisphenol A ° , and between poly(ethylene oxide) and a poly(ether sulphone) The above equations have also been reformulated in terms of the equation-of-state theory to obtain the interaction energy, which is concentration independent rather than the Flory-Huggins X parameter which is composition dependent. 

In contrast to other cleavage reagents, this anodic oxidation does not show stereochemical preference. In addition, ether derivatives are oxidized in similar current efficiencies to those of the parent 1,2-diols. Cyclohexene oxide is oxidized via the corresponding hydroxy ether. 

The alcoholysis of a-epoxides gives hydroxy ethers in a trans opening of the ring. An example is the treatment of cyclohexene oxide with methanol under reflux in the presence of a small quantity of sulfuric acid, trans-2-methoxycyclohexanol being formed in 82% yield. The mechanism and stereochemistry of the opening of oxide rings have been reviewed. ... 

Pentanediol is often superior to other diols such as 2,3-butanediol for these reactions because of higher distereoselectivities in reactions with nucleophiles and the more facile cleavage of the resulting hydroxy ether by oxidation-p-elimination. Removal of the chiral auxiliary is usually carried out with Pyri-dinium Chlorochromate oxidation followed by p-elimination using KOH, K2CO3, piperidinium acetate, dibenzylammonium trifluoroacetate, " or DBU. In some cases, 1,3-butanediol is preferred because the final 3-elimination may be effected under milder conditions. ... 

Corma et aL [239] took advantage of both redox and acidic properties of Ti/Al-MCM-41 (Si/Ti = 68 and Si/Al = 196) aluminosOicate to carry out the multistep oxidation of linalool to cyclic furan and pyran hydroxy ethers (Scheme 6). 

Benzylic methylene groups are more readily oxidized to benzyhc alcohols when compared to simple alkanes. Typical reagents include manganese-salen and PhIO ° or peroxides. a-Hydroxy ethers are also generated by reaction of this regents with ethers.A-Benzyl phthahmide reacts with NBS, NaOAc, and acetic... 

Two useful groups of related reactions may be discerned here, both of which are observed for prope-nyl-phenols. The first type is illustrated by the oxidation of isoeugenol (255) with aqueous iron(IIl) chloride,which yields the threo- and erythro-stereomers (55%) of the hydroxy ether (256), presum-... 

Isomers of 6,7-Epoxy-linalool as Precursors of Linalool Oxides. Previously, the triol (21) had been proposed as a possible precursor of the hydroxy ethers (14) and (15), the so-called linalool oxides(Fig-ure 8). At an acidic pH (<3.5) and/or during heat treatment (e.g., steam distillation/extraction), the triol (21) had been found to be decomposed to (14) and (15) (23,24). In these previous experiments no formation of the corresponding pyranoid linalool oxides (22) and (23) was observed. We evaluated the hypothesis that linalool oxides are formed from triol (21) under natural conditions of papaya pulp (i.e. pH 5.6) and could find no formation of linalool oxides. Even in model experiments carried out at pH 3.5, only traces of linalool oxides were detected after incubation of (21) for three days. As a result of these experiments the isomers of 6,7-epoxy-linalool have to be considered as the natural precursors of linalool oxides (14, 15) as recently suggested by Ohloff et al. (25). The latter s proposal was based on earlier findings obtained in a series of chemical reactions (9). 

Brocksom et al. have shown that isopulegols (e.g., 169) can be oxidized to the hydroxy ether 645 by thallium triacetate, without loss of stereochemistry. ... 

HYDROXY ETHER (111-15-9) Forms explosive mixture with air (flash point 117°F/ 47°C). Reacts violently with oxidizers. Incompatible with strong acids, nitrates. Softens many plastics. Attacks some rubber and coatings. 

Satpathi et al. [78] synthesized an AB2 monomer containing pendant -CF3 groups, namely bis-(4-fluoro-3-trifluoromethylphenyl)-4 -hydroxy-phenylphosphine oxide, which was self-condensed to afford fluorinated hb-poly(arylene ether phosphine oxide) (F-hb-PAEPO) (Scheme 2.19). A high molar mass of M 6,16,000 g/mol was achieved with D = 1.4. The F-hb-PAEPO was completely soluble in a wide range of organic solvents, namely CHCI3, CH2CI2, THF, NMP, DMF, DMSO, DMAc, and acetone at room temperature. 

In the ethyl (b) and isopropyl (d) series the p-hydroxy phosphine oxides were not separable but fortunately, the enol ethers could be resolved by (aminopropyl silica gel) MPLC. As shown in Scheme 11, the separation was less efficient in the ethoxy series providing oidy a 23/77 mixture of... 

The diastereoisomers of dihydropinol (127) (575, 541), which also have a cineole-like odor, as well as their probable precursors (-h)-dihydrocarveol and (— )-isodihydrocarveol [diastereoisomers (51)] 541, 542) are components of caraway oil. The diastereoisomeric linalool oxides (128) (furanoid) and (129) (pyranoid) have been found during the last few years in a large number of essential oils as important aroma-forming substances. In most cases these hydroxy ethers are accompanied by linalool (6) from which they may be formed in a suc-... 

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