Ozonides cross

If the Criegee mechanism operated as shown above, the cis/trans ratio for each of the two cross ozonides would have to be identical for the cis and trans alkenes, since in this mechanism they are completely cleaved. 

The unusually stable cross-ozonide 89 has been reported <06TA1780>, and a range of isomeric mono- and disulfoxides of the E-cyclooctene-derived 1,2,3-trithiolane 90 have been prepared <06T5441>. 

No cross ozonide was formed from unsymmetrical alkenes. The authors theorized628 that the carbonyl oxide zwitterionic species formed on wet silica gel immediately adds water followed by rapid decomposition of the intermediate hydroxyalkyl hydroperoxide to carboxylic acid and water. It means that water on silica gel acts as participating solvent. In the absence of adsorbed water, rapid recombination of the adsorbed aldehyde and carbonyl oxide due to a favorable proximity effect gives normal ozonide. The low mobility of adsorbed species on the silica surface accounts for the absence of cross ozonides. 

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... 

Bis-acyloxy-substituted 2-butynes 97 in the presence of added carbonyl compound (e.g., acetone) failed to give the corresponding cross-ozonides. Instead, the bicyclo[3.2.1]ozonides 98 were obtained in good yields by intramolecular cyclization of the CO intermediate with only one of the ester carbonyl groups. The bicyclo[2.2.1]ozonide 99 which... 

In the case of pyrene, there are two sextets and two fixed double bonds similar to the phenanthrenic double bond. In agreement with this argument and with the result for phenanthrene, co-ozonolysis of pyrene with formaldehyde or acetyl cyanide afforded the expected normal ozonide 114 and the cross-ozonide 115 with an aldehydic group. In a separate co-ozonolysis of 115 with vinyl acetate, diozonides 116 were prepared. No cross-ozonide was obtained in the presence of benzoyl cyanide, which afforded only the normal mono-ozonide 114 (Scheme 36 and Table 15). 

Cyclohexadiene yielded only the two (Z)-cross-ozonides with the upper one predominating. 1,3-Cycloheptadiene afforded the two (Z)-cross-ozonides with the lower one predominating, and 1,3-cyclooctadiene gave only the lower (Z)-cross-ozonide. At room temperature in CH2CI2, the CM-double bonds isomerize to /ram-configurations. 

It was established <2002T891> that in the presence of trifluoroacetophenone as trapping agent, the ozonolysis of 2,2,6-trimethyl-l-methylenecyclohexane afforded only the cross-ozonide derived from the capture of formaldehyde oxide, whereas the ozonolysis of 2,2,5-trimethyl-l-methylenecyclopentane gave only the alternative cross-ozonide derived from cycloadditions of 2,2,5-trimethylcyclopentanone oxide. 

The transformation of tetrasubstituted ethylenes into 1,2,4-trioxolanes may also be achieved if the ozonolysis is carried out in the presence of a foreign carbonyl compound as described in Section 4.33.3.4. With formaldehyde as added carbonyl compound, 3,3-disubstituted derivatives are obtained, whereas in the presence of excess ketone (e.g. by using the latter as solvent), the ozonolysis gives rise to tetrasubstituted 1,2,4-trioxolanes which are difficult to prepare by other methods. Reactions (163) -> (164) and (165) -> (166) provide two examples of this versatile 1,2,4-trioxolane synthesis. Unlike the parent system (2), alkyl- and/or aryl-substituted 1,2,4-trioxolanes generally are stable, non-explosive compounds. Mixtures of crossed ozonides (cf. Section 4.33.3.1.1) or of cis and trans isomers can be separated by thin layer, column or gas chromatography. The cis isomers of symmetrical 3,5-disubstituted 1,2,4-trioxolanes are meso forms, whereas the corresponding trans isomers represent racemates which in some cases have been resolved into their optical... 

We have shown that cross diperoxides can be formed by various ozonolysis procedures. We now hope to parallel the work done where cross ozonides were produced—i.e., to examine the influence of olefin stereochemistry and other reaction variables. 

This reaction scheme was supported by numerous direct and indirect experimental data. At low temperatures, primary ozonide was obtained [8] imder the action of ozone on asymmetrical olefins, cross ozonides are formed [9], This scheme and arguments for it were analyzed in detail in [1,2],... 

Loan, L. D., R. W. Murray, and P. R. Story. 1965. The mechanism of ozomolysis formation of cross ozonides. Journal of the American Chemical Society 87 737. 

Cross Ozonides from Pairs of Symmetrical Olefins... 

Failure to find the two symmetrical or cross ozonides for 3-heptene led Criegee to postulate a solvent cage (2) which prevented the cleavage fragments from participating in exchange or cross reactions. More recently a number of reports (5, 8, 9,10,11,12,13,14) have indicated that cross ozonides can be produced for several unsymmetrical olefins. The fact that the percentage cross ozonide produced decreases with olefin concentration (8) possibly indicates that the earlier failures to find cross ozonides may simply have been caused by the olefin concentration used. 

The observations of symmetrical cross ozonides from unsymmetrical olefins suggest that unsymmetrical cross ozonides ought to be produced from pairs of symmetrical olefins. Criegee had examined this point earlier (2) and found that no detectable amounts of 3-heptene ozonide were produced when a mixture of 3-hexene and 4-octene was ozonized. Again, this may have been a result of the particular olefin concentrations used. The recent observations that ozonide cis-trans ratios in both cross ozonides (5, 10, 11) and normal ozonides 4-14) can depend on olefin stereochemistry as well as steric factors in the olefin 11) prompted us to reinvestigate the possibility of obtaining unsymmetrical ozonides from pairs of symmetrical olefins. Such an investigation presents an opportunity to examine ozonide cis-trans ratios and yields where several new reaction variables are possible. 

Targely based on our finding that the cis/trans ratios of cross ozonides 10) formed from unsymmetrical olefins depended on olefin geometry 11, 12), we have proposed a new mechanism of ozonolysis which takes account of this effect 14). The new mechanism, which considers only a limited type of olefin, namely trans-disubstituted and relatively unhindered cis olefins, differs significantly from the generally accepted Criegee mechanism 1,5). 

In our view, cross ozonides may be formed by the typical sequence below in which aldehyde (4), produced in the reaction, reacts with molozonide (2) in an aldehyde interchange reaction to yield ozonide (5). As demonstrated previously, the molozonide-aldehyde interchange mechanism 12, 14), from consideration of steric interactions, correctly predicts that cis-olefin will generate relatively more cis-ozonide than will the corresponding trans-olefin. This interpretation does not refer to the absolute values of the cis/trans ratios. 

There is no evidence indicating that the zwitterion reacts in this fashion, and it would not account for the dependence of cross ozonide stereo-isomeric ratios on olefin geometry. We have experiments underway to check this possibility, however.)... 

When appreciable concentrations of carbonyl compounds are present before complete formation of ozonide, crossed ozonides are formed. This occurs when the added carbonyl compound traps the zwitterion formed in the cleavage step. When c -stilbene is subjected to ozonolysis in the presence of 0-labeled benzal-dehyde, the label is incorporated into the ether rather than the peroxide portion of the ozonide ... 

This result is consistent with formation of the crossed ozonide via the cleavage-recombination mechanism ... 

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