Unsaturated carbonyl compounds, ozonolysis

The structure of the ozonide from the reaction of the allylic alcohol 13 with ozone is shown below. This is the normal product from ozonolysis. Notice that there is no oxidant (such as H2O2) or reductant (such as Mc2S) in the formation of the keto-acid 14. The formation of the product 14 can be explained by fragmentation of the ozonide (see below), which occurs in a similar way to that described for the ozonolysis of a,p-unsaturated carbonyl compounds given in Scheme 5.105. See R. L. Cargill and B. W. Wright, / Org. Chem., 40 (1975), 120. 

A review of mechanisms of ozonolysis of unsaturated carbonyl compounds and alcohols has addressed effects of the substrate structure and reaction conditions on the product composition. " ... 

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. 

Unsaturated 1,5-dicarbonyl compounds. The phenylthioalkylation of silyl enol ethers of carbonyl compounds (9, 521-522) can be extended to the synthesis of unsaturated 1,5-dicarbonyl compounds. In a typical reaction the enol silyl ether of a ketone is alkylated with the unsaturated chloride 1 under ZnBr2 catalysis to give a homoallyl sulfide. Ozonolysis of the methylene group is accompanied by oxidation of the phenylthio group sulfoxide elimination results in an unsaturated 1,5-aldehydo ketone (equation I). Alkylation with 2 results in a methyl ketone (equation II). 

Ozonolysis of intermediate nitronate anions also yields carbonyl compounds,and, while unsaturation and acetal groups cannot be tolerated, other sensitive molecules have been prepared using this reaction (equation 13). ... 

Chiral -substituted carbonyl compounds have been prepared in high optical purity (64-98%) by the use of organoaluminium chemistry. Thus treatment of an acetal derived from an a, 6-unsaturated aldehyde and R,R- tartaric acid diamide with a trialkylalane gives largely the 1,4- addition product from which the desired ketone is derived by ozonolysis (Scheme 12). 1... 

Ozone plays a major role in the degradation of unsaturated VOCs in the troposphere, especially during night-time. The rate constants of the ozonolysis of a variety of alkenes have been reported [1]. However, in most instances the fate of the primary products of the ozonolysis is unknown, although the secondary reaction products are of crucial importance for the overall understanding of the alkene/ozone chemistry. The classical Criegee mechanism of the ozonolysis reaction involves the primary ozonide (POZ, 1,2,3-trioxolane), which cleaves to the Criegee intermediate (carbonyl O oxide) and a carbonyl compound [2, 3]. The secondary ozonide (SOZ, 1,2,4-trioxolane) is formed from these components in a [l,3]-dipolar cycloaddition reaction. 

The mechanism proposed by Criegee best describes the degradation initiated by ozone called ozonolysis. Ozone, a very reactive material, reacts at the surface, across the double bond, in an unsaturated polymer to form a trioxolane stmcture. This stmcture undergoes decomposition to give a carbonyl compound and a zwitterion, resulting in a severed molecular chain. The zwitterion can recombine to form either an ozonide, diperoxide, or higher peroxide. 

Ozonolysis was once used to locate the position of a double bond (or bonds) in unsaturated compounds of unknown structure—largely because of the ease of characterisation of the carbonyl products— but has now been superseded by physical methods, e.g. n.m.r. spectroscopy, which are easier and quicker. Benzene forms a triozonide which decomposes to yield three molecules of glyoxal, OHC—CHO the sole reaction of benzene that suggests it may contain three real double bonds in a Kekule structure Alkynes also undergo ozonolysis, but at a much slower rate than alkenes. 

With respect to polymer synthesis and to the development of biologically active compounds in recent years, the ozonolysis/reductive cleavage of OA or MO or the fragmentation of the intermediary carbonyl oxide to 9-oxononanoic acid and its respective methyl ester gained attention again [33-39]. 9-Oxononanoic acid can be easily converted to 9-amino- or 9-hydroxynonanoic acid as sources for polyamides and polyesters [40]. A French patent claimed the synthesis of oxo-nonanoic acid via homometathesis of OA, followed by reductive ozonolysis of the unsaturated C18 diacid obtained [41]. 

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