Ozonide intermediate

This cleavage reaction is more often seen in structural analysis than in synthesis The substitution pattern around a dou ble bond is revealed by identifying the carbonyl containing compounds that make up the product Hydrolysis of the ozonide intermediate in the presence of zinc (reductive workup) permits aide hyde products to be isolated without further oxidation... 

Trioxolanes are key intermediates in the ozonolysis of alkenes (Section 4.16.8.2). This reaction is of considerable importance in synthetic chemistry where ozonide intermediates are often reduced (to aldehydes or alcohols) or oxidized (to carboxylic acids) in situ. Advantage has been taken of the stability of certain derivatives to investigate selective chemical reactions. An example of selective reduction is shown in Scheme 47 <91TL6454> with other uses of the 1,2,4-trioxolane ring as a masked aldehyde or ester referred to in Section 4.16.5.2.1. 

The reactivity of ozone reflects two modes of oxidation non-selective free radical reactions involving hydroxyl radical, and the selective addition of ozone to form an ozonide intermediate and eventually various carbonyls and carboxylic adds (46). The latter sequence, known as ozonolysis, is shown below for anthracene. 

If the reaction is carried out in an emulsion of sodium hydroxide and hydrogen peroxide, the ozonide intermediates are converted to carboxylic acids directly, wiA a consequent increase in yields. 

Ozonolysis as used below is the oxidation process involving addition of ozone to an alkene to form an ozonide intermediate which eventually leads to the final product. Beyond the initial reaction of ozone to form ozonides and other subsequent intermediates, it is important to recall that the reaction can be carried out under reductive and oxidative conditions. In a general sense, early use of ozonolysis in the oxidation of dienes and polyenes was as an aid for structural determination wherein partial oxidation was avoided. In further work both oxidative and reductive conditions have been applied . The use of such methods will be reviewed elsewhere in this book. Based on this analytical use it was often assumed that partial ozonolysis could only be carried out in conjugated dienes such as 1,3-cyclohexadiene, where the formation of the first ozonide inhibited reaction at the second double bond. Indeed, much of the more recent work in the ozonolysis of dienes has been on conjugated dienes such as 2,3-di-r-butyl-l,3-butadiene, 2,3-diphenyl-l,3-butadiene, cyclopentadiene and others. Polyethylene could be used as a support to allow ozonolysis for substrates that ordinarily failed, such as 2,3,4,5-tetramethyl-2,4-hexadiene, and allowed in addition isolation of the ozonide. Oxidation of nonconjugated substrates, such as 1,4-cyclohexadiene and 1,5,9-cyclododecatriene, gave only low yields of unsaturated dicarboxylic acids. In a recent specific example... 

Li12[Mnn2ZnW (ZnW90 34)2] Alkanes, alkylarenes Ketones, a-oxidation products Ozone h2o Likely metal-ozonide intermediate 461... 

Alkanes and aromatic compounds are less readily oxidized than alkenes, but can be made to react with ozone at higher temperatures to give a chemiluminescence emission. This difference in reactivity can be exploited to increase selectivity. For example, a postcolumn reactor at 100°C allows only the detection of alkenes, but when the temperature is increased to 150°C aromatic compounds will also elicit chemiluminescence and at 250°C all other hydrocarbons will give rise to emission. Aromatic compounds are likely to react in a similar way to alkenes, by forming an ozonide intermediate. The reaction pathway for the ozone-mediated chemiluminescence of alkanes is unknown and results in much lower chemiluminescence intensity. The detector response is linear when ozone is present in excess and absolute... 

The first step of the ozonolysis mechanism is the initial electrophilic addition of ozone to the C=C double bond to form the molozonide intermediate. Its instability leads to a further reaction, producing a carbonyl and carbonyl oxide molecule (Scheme 2.10, II). The carbonyl and carbonyl oxide rearrange to create the stable ozonide intermediate (Scheme 2.10, III). A reductive workup is then undertaken to convert the ozonide specie into carbonyl products (Scheme 2.10,1) [19]. 

The precursor to A was treated with ozone at -78°C and the resulting ozo-nide was treated with dimethyl sulfide to give A. Given the following spectral data, draw the structure of the precursor as well as the ozonide intermediate ... 

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