Ethers Dimethyl ether Epoxides

The photodecomposition of oxiran and alkyloxirans both in the gas phase and in solution has been extensively investigated. Processes arising by carbon-oxygen bond homolysis and hydrogen abstraction have been reported, and the subject has been reviewed in detail elsewhere.48 The most recent studies include the photoaddition of methanol to alicyclic epoxides, a process that appears to be promoted by acid,49 and the interesting if unusual photochemically induced conversion of the epoxyalcohol (56) to sugiresinol dimethyl ether (57).50... 

A regioselective and highly syn-stereoselective catalyst-free intermolecular alkylation of aryl borates with aryl epoxides under mild, neutral conditions has been reported.27 The reaction of /ra .s-stilbene oxide with tri(3,5-dimethylphenyl)borate gave a 38% yield (>95% syn) of the C-alkylated product (13), easily separated from (g) the O-alkylated product(s). Triflic anhydride has been used to activate enones to nucleophilic attack by electron-rich arenes in the presence of a sterically hindered base.28 Resorcinol dimethyl ether, for example, reacted with cyclohex-2-en-l-one to... 

As the key precursor towards the realization of 1,7-epoxy cyclononanes and 1,8-epoxycyclodecanes, an 1 l-oxatricyclo[6.2.1.02,6]decane skeleton was constructed by using the Hoffmann [4+3] cycloaddition methodology <07EJO4383>. In Majetich s total synthesis of (-)-salviasperanol, the key step was the trifluoroacetic acid-promoted isomerization of a vinyl epoxide to 2,5-dihydrofuran, whose O-thiocarbamate was removed by radical reaction to produce salviasperanol dimethyl ether <07OL85>. The synthetic route is depicted below. 

Cp2TiCl-mediated 5-exo-trig cyclizations have been intensively exploited by Roy et al. for the total synthesis of ( )-dihydroprotolichesterinic and ( )-roccellaric acids, ( )-sesamin, ( )-dihydrosesamin, ( )-acuminatin, ( )-eudesmin, ( )-lariciresinol, ( )-pinoresinol, ( )-piperitol, ( )-acumi-natin methyl ether, (zh)-sanshodiol methyl ether, ( )-piperitol methyl ether, ( )-pinoresinol monomethyl ether, ( )-lariciresinol monomethyl ether, and ( )-lariciresinol dimethyl ether [ 100-103]. Moreover, this group has very recently reported the enantioselective synthesis of (-)-sesamin (Scheme 19), (-)-dihydrosesamin, (-)-acuminatin, and (-)-methyl piperitol by radical cyclization of chiral epoxides initiated by Cp2TiCl [104]. 

METHYLENE BROMIDE (74-95-3) CHiBr2 Noncombustible liquid. Incompatible with some alkali metals amines, azo/diazo compounds dialkylzincs, dimethyl sulfoxide, dimethyl formamide, epoxides such as glycidol, ethylene glycol diethyl ether, ethers, nitrides. Mixture with potassium produces a sensitive impact-sensitive explosive material and may react with other metals, forming dangerous materials. 

Thus, the aldol shown, which is susceptible to Sharpless-type epoxidation, has been obtained from phytal and the protected hydroquinone (ref. 120). Formation of the epoxide presumably with a chiral peracid (or perhaps with a conventional peracid relying on the asymmetry of the substrate) and then cleavage reductively in t-butyl methyl ketone containing lithium aluminium hydride led to a diol. The benzylic hydroxyl group of this was hydrogenolysed to afford the hydroquinone dimethyl ether in 85% yield. Ceric ammonium nitrate (CAN) oxidation afforded the intermediate benzoquinone hydrogenation of which was reported to result in 2R,4 R,8 R-a-tocopherol by, presumably, avoidance of a racemisation step. 

An epoxidizing agent that has found widespread use is dimethyl dioxirane (DMDO). The reagent is generated from acetone and Oxone , a source of potassium peroxomonosulfate (KHSO5) (5.50). Epoxidation with DMDO occurs under mild, neutral conditions, without any nucleophilic component, which is ideal for preparing sensitive epoxides. For example, the enol ether 41 was epoxidized selectively using DMDO (5.51). ... 

A mixture of the epoxide ca. 5 mmol), sodium azide (6 g, activated by the method of Smith) and 0.25 ml of concentrated sulfuric acid in 70 ml of dimethyl sulfoxide is heated in a flask fitted with a reflux condenser and a drierite tube on a steam bath for 30-40 hr. (Caution carry out reaction in a hood.) The dark reaction mixture is poured into 500 ml of ice water and the product may be filtered, if solid, and washed well with water or extracted with ether and washed with sodium bicarbonate and the water. The crude azido alcohols are usually recrystallized from methanol. 

Phenols and primary alcohols form ethers when heated with dicyclohexylcarbo-diimide (DCC see 10-23). 1,2-Diols can be converted to epoxides by treatment with dimethylformamide dimethyl acetal, (MeO)2CHNMc2, with diethyl azodi-carboxylate, EtOOCN=NCOOEt, and Ph3P with a diaUcoxytriphenylphospho-rane, ° or with TsCl-NaOH-PhCH2NEt3+ CP. ... 

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