Ozone oxidative cleavage

Oxidative cleavage of olefins is frequently a useful procedure synthetically as well as analytically. Ozonization is an effective means of carrying out such a cleavage under... 

Alkenes with at least one vinjdic hydrogen undergo oxidative cleavage when treated with ozone, yielding aldehydes (Section 7.9). If the ozonolysis reaction is carried out on a cyclic alkene, a dicarbonyl compound results. 

Stearolic acid, C H- Oa, yields stearic acid on catalytic hydrogenation and undergoes oxidative cleavage with ozone to yield nonanoic acid and nonanedioic acid. What is the structure of stearolic acid ... 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

As inert as the C-25 lactone carbonyl has been during the course of this synthesis, it can serve the role of electrophile in a reaction with a nucleophile. For example, addition of benzyloxymethyl-lithium29 to a cold (-78 °C) solution of 41 in THF, followed by treatment of the intermediate hemiketal with methyl orthoformate under acidic conditions, provides intermediate 42 in 80% overall yield. Reduction of the carbon-bromine bond in 42 with concomitant -elimination of the C-9 ether oxygen is achieved with Zn-Cu couple and sodium iodide at 60 °C in DMF. Under these reaction conditions, it is conceivable that the bromine substituent in 42 is replaced by iodine, after which event reductive elimination occurs. Silylation of the newly formed tertiary hydroxyl group at C-12 with triethylsilyl perchlorate, followed by oxidative cleavage of the olefin with ozone, results in the formation of key intermediate 3 in 85 % yield from 42. 

The chiral auxiliary can be removed by oxidative cleavage of the double bond with ozone <00TL787>. 

The ozonolysis of cyclobutene derivatives in the preparation of 1,4-diketones was also applied to the total synthesis of eyclopentanoid antibiotics 161 162k The oxidative cleavage of (470) by ozone and reductive work-up yielded the diketone (471) in 73 % yield. Diketone (471) underwent intramolecular aldol cyclization to give the key intermediate (472), which was used to synthesize ( )-xanthocidin161,162), (+)-epi-xanthocidin 162), ( )-p-isoxanthocidin161,162) as well as ( )-desdihydroxy-4,5-didehydroxanthocidin162). 

Oxidative cleavage of the double bond of 9 with ozone provided the expected dialdehyde which was unstable and readily underwent expected aldol condensation to give the desired aldehyde 10 when treated with 7V-methylanilinium trif-luoroacetate [5]. 

From Isosafrole. For many years, oxidative cleavage of isosafrole was the only route applicable on an industrial scale. Examples of oxidants that give good yields of heliotropin are chromium(VI) salts, oxygen, and ozone. 

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... 

In previous studies, i,e. concurrent carbonyl-oxygen exchange in the hydrolysis of esters, acid hydrolysis of orthoesters and oxidation of acetals by ozone, the configuration of the tetrahedral intermediate was determined by the application of the principle of stereoelectronic control. There could be some ambiguity in these experiments as the theory of stereoelectronic control is used to predict both the stereochemistry of the tetrahedral intermediate as well as its breakdown. The oxidation cleavage of vinyl orthoesters can therefore be considered a more powerful experimental technique in that respect because the configuration of the hemi-orthoester... 

Alkyl-s-caprolactones are formed (Scheme 10) in good overall yields (up to 75%) and with high enantiomeric purity (ee = 90%, 94%) by alkylation of SAMP-hydrazones 25 (SAMP = (A)-l-amino-2-methoxymethylpyrrolidine) and subsequent oxidative cleavage of the hydrazone 26 with ozone <1995S947>. 

A comparative study involving singlet oxygen, ozone, and 4-phenyl-1,2,4-triazoline-3,5-dione oxidation of chiral oxazolidinone substituted enecarbamates has shed light on the mechanistic intricacies of the oxidative cleavage of alkenyl double bonds.282... 

The reactivity of unsaturations with ozone has been applied to produce structures which allow subsequent degradation of materials by ozonolysis. In this way, Peters et al. [105] prepared polyurethanes using novel unsaturated diisocyanates which can be degraded by oxidative cleavage of the double bonds. 

Malonate was used in the synthesis,2 and it makes sense to add the more reactive alkyl group last in this case the allyl group. The oxidative cleavage was done with ozone. 

The synthesis of 18 is discussed in the next chapter. The synthesis of 14 is a classic of its kind the alcohol 17 is not isolated but dehydrated directly to the cyclohexene 16 and the oxidative cleavage is done by ozone. The intramolecular aldol is unambiguous as the alternative is a seven-membered ring.2... 

Such processes are always accompanied by a DP loss, either by electrophilic attack of ozone, by an ozone-catalyzed cleavage of the glycosidic bond or by attack of secondary radical species [15]. Residual lignin also plays a crucial role in ozone bleaching. Model studies showed that lignin with free phenolic hydroxyl groups accelerated carbohydrate oxidation, probably by activation of oxygen via phenoxyl radicals, whereas etherified phenolic model compounds had a protective effect [16,17]. 

Fig. 17.32. Oxidative cleavage of an asymmetric ketone with complementary regiose-lectivities. Lactone A is obtained by Baeyer-Villiger oxidation of menthone [2-methyl-5-(l- methylethyl)cyclo-hexanone]. Alternatively, one may first convert menthone into the silylenol ether B and cleave its C=C double bond with ozone to obtain a silyl ester containing an a-methoxyhydroperoxide group as a second functional group (which resembles the unstable structural element of the so-called ether peroxides cf. Figure 1.38). The latter is reduced with NaBH4tothe hydroxylated silyl ester C. The hydroxycarboxylic acid is obtained by acid-catalyzed hydrolysis. It cyclizes spontaneously to give lactone D.

Base-catalysed conjugate addition of nitropropane to methyl vinyl ketone occurred smoothly to give the nitroketone. Formation of the salt with sodium methoxide was followed by oxidative cleavage of the C-N linkage with ozone. The product was a 1,4-diketone which was isolated without further aldol reaction by this route. 

Ozone causes oxidative cleavage of the double bonds in rubber and breaks the polymer chain. 

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