Ozonation of Feist’s ester

The ozonation of Feist s ester yields three products 2,3-dicarbomethoxytetrahydrofuran-4-one (III), 3,4-dicarbome-thoxy-5-hydroxy-2-oxa-2,3-dihydropyran (IV), and 4,5-di-carbomethoxy-l-oxaspiro[2.2 pentane (V). Structures were assigned primarily through spectroscopic evidence (mass, NMR, and infrared spectra). The last of these compounds is probably not a direct ozonation product (stoichiometry and trapping studies). A mechanism is proposed in which the initial step is formation of a primary ozonide. From that stage, the breakdown is abnormal. 

Product Analysis. Quantitative analysis for each of the products of the ozonation of Feist s ester was carried out by an NMR method (Varian HA60). The solvent for the ozonation was evaporated in vacuo, a suitable internal standard (usually f erf-butyl benzoate), was added and the spectra were determined and integrated in chloroform-d. All analyses were reproducible to 10%. 

Story et al. have suggested that VIII might be the important intermediate in the ozonation of Feist s ester (11). 

If this is the intermediate, other methylenecyclopropanes should give ozonation products similar to those found in the ozonation of Feist s ester. Since they do not and because our evidence indicates that the epoxide is not a primary product, the mechanism of Story et al. does not seem to apply to this reaction. 

T he structure of Feist s acid, la, was determined with certainty some 60 years after its preparation (1—6). More recently, the proposal that the ozonation product of Feist s ester (lb) had structure II was shown to be incorrect (7). Our initial report not only showed that no II was present in any ozonation of Feist s ester but offered chemical and spectroscopic proof for III as a major ozonation product. 

This paper is concerned with the structure proof of each of the major products of the ozonation of the methyl ester of Feist s acid. Other data pertaining to the mechanism of this unusual ozonation are presented, and a mechanism is hypothesized. 

The epoxide is not a primary product both the stoichiometry and the tetracyanoethylene experiments indicate that it is formed from attack of an intermediate on unreacted Feist s ester. For example, less than 1 mole of ozone per mole of Feists ester is required for all ozonations—with the less reactive solvents, such as methylene chloride and Freon 11, the deficiency in ozone required is approximately equal to the amount of epoxide formed. Addition of tetracyanoethylene before ozonation results in an ozonation of normal stoichiometry with no epoxide being formed. 

If the reaction is stopped before completion, the relative amounts of IV formed are greatly decreased. This suggests to us that the initial ozonation product has several modes of decomposition available, and that reaction with Feist s ester (or tetracyanoethylene) is more rapid than unimolecular decomposition. 

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