Oxidation of Alkenes Cleavage to Carbonyl Compounds

Interactive to use a web-based palette to predict products from the oxidation of alkenes. 

In all the alkene addition reactions we ve seen thus far, the carbon-carbon double bond has been converted into a single bond but the carbon skeleton has been left intact. There are, however, powerful oxidizing reagents that will cleave C=C bonds and produce two carbonyl-containing fragments. 

Low -molecular-weight ozonides are explosive and are theretore not isolated. Instead, the ozonide is immediately treated with a reducing agent such as zinc metal in acetic acid to convert it to carbonyl compounds. The net result of the ozonolysis/reduction sequence is that the C=C bond is cleaved and oxygen becomes doubly bonded to each of the original alkene carbons. If an alkene with a letrasubstituted double bond is ozonized, two ketone fragments result if an alkene with a trisubstituted double bond is ozonized, one ketone and one aldehyde result and so on. 

What alkene would yield a mixture of cyclopentanone and propana) on treatment with ozone followed by reduction with zinc  

What products would you expect from reaction of l-methy)cyc)ohexene with the following reagents  

Problem 7,17 Propose structures for alkenes that yield the following products on reaction with ozone followed by treatment wdth Zn  

What alkene would yield a mixture of cyclopentanone and propanal on treatment 

WORKED EXAMPLE 8.3 Predicting the Reactant in an Ozonolysis Reaction 

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Chromium trioxide adsorbed on silica or alumina has been used for the oxidative cleavageof alkenes to aldehydes or ketones with little or no formation of carboxylic acids. A solution of bis(triphe-nylsilyl) chromate has also been used for the selective cleavage of double bonds to carbonyl compounds. ... 

Thermal decomposition of oxetanes proceeds at elevated temperatures, usually in the range of 300-450 °C, to give an alkene and a carbonyl compound in practically quantitative yield. Gas phase thermolyses of several alkyl-substituted oxetanes have been studied in detail, because such compounds occur as intermediates in the oxidation of alkanes (Section 5.13.3.3). When the oxetane is unsymmetrically substituted, as in the case of 2,4-dimethyl-oxetane (20), two modes of cleavage, to give two different sets of products, are possible and are generally observed. In fact, when only hydrogen and alkyl substituents are present,... 

Palladium-catalyzed allylic oxidations, in contrast, are synthetically useful reactions. Palladium compounds are known to give rise to carbonyl compounds or products of vinylic oxidation via nucleophilic attack on a palladium alkene complex followed by p-hydride elimination (Scheme 9.16, path a see also Section 9.2.4). Allylic oxidation, however, can be expected if C—H bond cleavage precedes nucleophilic attack 694 A poorly coordinating weak base, for instance, may remove a proton, allowing the formation of a palladium rr-allyl complex intermediate (89, path by694-696 Under such conditions, oxidative allylic substitution can compete... 

Oxidation of alkenes with ozone followed by cleavage of the resulting ozonides to carbonyl compounds is widely used for the determination of structure of unsaturated compounds. The ozonolysis technique is described in detail in Section 2.17.4, p. 103. 

The results of some oxidations with potassium permanganate differ depending on the pH of the reaction. For example, stearolic acid gives 9,10-diketostearic acid at pH 7-7.5 (achieved with carbon dioxide) and azelaic acid on treatment at pH 12 [864]. In some reactions, potassium permanganate is used as a catalyst for oxidation with other oxidants, such as sodium periodate. Thus alkenes are cleaved to carbonyl compounds or acids via vicinal diols obtained by hydroxylation with potassium permanganate, followed by cleavage by sodium periodate [763, 552]. 

NR s not reactive toward hydrocarbons S = stereoselective epoxidation E = epoxidation HA = hydroxylation of alkanes OA = oxidation of alcohols to carbonyl compounds PO oxidation of phosphines to phosphine oxides OC = oxidative cleavage of alkenes K= ketonization of alkenes DO = hydroxylation of alkenes to diols AO al1ylic oxidation of alkenes. 

The synthetically most valuable intermediate in heterofullerene chemistry so far has been the aza[60]fulleronium ion C59N (28). It can be generated in situ by the thermally induced homolytic cleavage of 2 and subsequent oxidation, for example, with O2 or chloranil [20-24]. The reaction intermediate 28 can subsequently be trapped with various nucleophiles such as electron-rich aromatics, enolizable carbonyl compounds, alkenes and alcohols to form functionalized heterofullerenes 29 (Scheme 12.8). Treatment of 2 with electron-rich aromatics as nucleophilic reagent NuH in the presence of air and excess of p-TsOH leads to arylated aza[60]fullerene derivatives 30 in yields up to 90% (Scheme 12.9). A large variety of arylated derivatives 30 have been synthesized, including those containing cor-annulene, coronene and pyrene addends [20, 22-25]. 

Ozonolysis of cyclic olefins in the presence of carbonyl compounds gives the corresponding cross-ozonides.1329 In the ozonation of 1,2,4,5-tetramethyl-1,4-cyclohexadiene, oxidative dehydrogenation (formation of 1,2,4,5-tetramethylben-zene) was found to compete with oxidative cleavage because of steric hindrance.1330 Secondary ozonides (the 76 1,2,4-trioxolanes) are formed in high yields in the gas-phase, low-temperature ozonation of terminal and disubstituted alkenes.1331... 

Ruthenium tetroxide is a four-electron oxidant which directly transforms alkenic compounds into oxidative cleavage products, i.e. carbonyl compounds and carboxylic acids.288 The reaction can be visualized as proceeding according to a [4 + 2] cycloaddition of the cis-dioxo moiety with the alkene, resulting in the formation of a RuVI cyclic diester which decomposes to ruthenium(IV) dioxide and oxidative cleavage products (equation 114).288 This reaction can be made catalytic... 

Ozonolysis allows the cleavage of alkene double bonds by reaction with ozone. Depending on the work up, different products may be isolated reductive work-up gives either alcohols or carbonyl compounds, while oxidative work-up leads to carboxylic acids or ketones. 

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