Epoxides conversion into carbonyl compounds

Ylides based upon sulfur are the most generally useful in these cyclopropane-forming reactions.133 Early work in this area was done with the simple dimethyloxysulfonium methylide (9) derived from dimethyl sulfoxide. The even simpler dimethylsulfonium methylide (10) was studied at the same time as a reagent primarily for the conversion of carbonyl compounds into epoxides.134 Somewhat later, other types of sulfur ylides were developed, among which the nitrogen-substituted derivatives such as (11) are... 

The deoxygenation of epoxides is not of great preparative value since it involves some loss of stereochemical integrity and the alkenes produced are more readily approached in other ways. Reductive cleavage of ozonides, for example, using triphenylphosphine, commonly forms part of the ozonolysis procedure for conversion of alkenes into carbonyl compounds. If a carbonyl compound is treated with an appropriate P(III) reagent then the reverse process may occur—reductive coupling to form a new C=C double bond. This has found a particularly important... 

Tri(organoseleno)boranes 35 are prepared from boron trihalides and organic selenolates as stable compounds (Scheme 35) [63]. These selenoboranes have been shown to be useful for the conversion of carbonyl compounds into seleno-acetals 36 [64] and the selective ring opening of epoxides [65]. Recently, it was reported that tri(phenylseleno)borane reacts with cyclic ethers to produce m-hydroxyalkyl phenyl selenides 37 in the presence of a catalytic amount of Lewis acid [43]. 

The conversion of epoxides into carbonyl compounds is an irreversible reaction. At 400° ethylene oxide (oxirane) passes into acetaldehyde, and at 500° propylene oxide (1-methyloxirane) gives a 2 1 mixture of propion-... 

Epoxides via methyl selenoacetals. Krief et al. have reported the synthesis of epoxides from two carbonyl compounds. The first step involves preparation of a dimethyl selenoacetal (1), followed by conversion to an a-methyl seleno-carbanion (a). These highly reactive carbanions react with even hindered carbonyl compounds to give 0-hydroxy methyl selenides (2), which are converted into selenonium salts by reaction with methyl iodide or dimethyl sulfate. 

Epoxidation of vinylsilanes will lead to silyl epoxides, which can be transformed into the carbonyl compounds 168 and 169 upon treatment with acid (equations 143 and 144)36,257,258 Conversion of the vinylsilane 170 into methyl enol ether 171 has recently... 

Sodium hypochlorite is used for the epoxidation of double bonds [659, 691] for the oxidation of primary alcohols to aldehydes [692], of secondary alcohols to ketones [693], and of primary amines to carbonyl compounds [692] for the conversion of benzylic halides into acids or ketones [690] for the oxidation of aromatic rings to quinones [694] and of sulfides to sulfones [695] and, especially, for the degradation of methyl ketones to carboxylic acids with one less carbon atom [655, 696, 697, 695, 699] and of a-amino acids to aldehydes with one less carbon [700]. Sodium hypochlorite is also used for the reoxidation of low-valence ruthenium compounds to ruthenium tetroxide in oxidations by ruthenium trichloride [701]. 

The oxidative cleavage of carbon-carbon bonds in vicinal diols [756, 759] is a reaction widely used in saccharide chemistry. Besides its application in this reaction, periodic acid achieves the oxidative coupling [757] or oxidation to quinones [758] of polynuclear aromatic hydrocarbons, the oxidation of methyl groups in aromatic compounds to carbonyl groups [760], the conversion of epoxides into dicarbonyl compounds [761], and the oxidative cleavage of trimethylsilyl ethers of acyloins to carboxylic acids [755]. 

The incorporation of Ti into various framework zeolite structures has been a very active research area, particularly during the last 6 years, because it leads to potentially useful catalysts in the oxidation of various organic substrates with diluted hydrogen peroxide [1-7]. The zeolite structures, where Ti incorporation has been achieved are ZSM-5 (TS-1) [1], ZSM-11 (TS-2) [2] ZSM-48 [3] and beta [4]. Recently, mesoporous titanium silicates Ti-MCM-41 and Ti-HMS have also been reported [5]. TS-1 and TS-2 were found to be highly active and selective catalysts in various oxidation reactions [6,7]. All other Ti-modified zeolites and molecular sieves had limited but interesting catalytic activities. For example, Ti-ZSM-48 was found to be inactive in the hydroxylation of phenol [8]. Ti-MCM-41 and Ti-HMS catalyzed the oxidation of very bulky substrates like 2,6-di-tert-butylphenol, norbomylene and a-terpineol [5], but they were found to be inactive in the oxidation of alkanes [9a], primary amines [9b] and the ammoximation of carbonyl compounds [9a]. As for Ti-P, it was found to be active in the epoxidation of alkenes and the oxidation of alkanes and alcohols [10], even though the conversion of alkanes was very low. Davis et al. [11,12] also reported that Ti-P had limited oxidation and epoxidation activities. In a recent investigation, we found that Ti-P had a turnover number in the oxidation of propyl amine equal to one third that of TS-1 and TS-2 [9b]. As seen, often the difference in catalytic behaviors is not attributable to Ti sites accessibility. 

Similar polymeric electrolysis conditions are able. In the presence of water, to effect the conversion of olefins Into epoxides (68), In this case, choice of an anion exchange resin was crucial (Amberllte IRA-900 br)). The electrochemical efficiency is substantially lower (due to the competing electrolysis of water) but yields are high. Unsaturated carbonyl compounds do not react. 

Aldol reaction between a silyl enol ether and an aromatic or aliphatic aldehyde can be catalysed by tetrabutylammonium fluoride ketones and epoxides are not attacked by the enolates derived in this manner. Directed cross-aldol reactions have now been carried out by conversion of a methyl ketone into the intermediate (15) using 9-trifluoromethylsulphonyl-9-borabicyclo[3,3,l]nonane and t-amine prior to reaction with the second carbonyl compound. ... 

Reactions.—The reaction of sulphonium ylides with carbonyl compounds to form oxirans is now a standard reaction. Among the more unusual examples reported are an intramolecular version directed towards the preparation of arene epoxide (12) (not isolable), the synthesis of the epoxide of 8-phenylthio-methylenecycloheptane, and the direct conversion of a diketone by dimethyl-sulphonium methylide into a doubly homologated hydroxymethyl aldehyde (13) by the rearrangement shown. ... 

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