Isomerization final ozonides

One of the most important features of the ozonolysis reaction of alkenes is one in which ozone adds to the C=C bond to form a primary ozonide (1,2,3-trioxolane). The Criegee mechanism suggests that this unstable intermediate decomposes into a carbonyl compound and a carbonyl oxide that recombine to form a final isomeric ozonide (1,2,4-trioxolane). Direct spectroscopic evidence for a substituted carbonyl oxide has only recently been reported by Sander and coworkers for the NMR characterization of dimesityl carbonyl oxide. Kraka and coworkers have theoretically modeled dimesityl carbonyl oxide and confirmed the structural aspects reported by Sander and coworkers on the basis of NMR data. 

The ozonide 287 resulting from a singlet oxygen reaction with 288 in methanol is converted to 289 by transannular epoxidation of the benzene ring. This oxide undergoes cis-trans isomerization to 290, and subsequent intramolecular Diels-Alder addition finally yields the novel product 291.166... 

Arylcyclopropanes and their heterocyclic analogues are liable to electron transfer induced fragmentation of a carbon-carbon bond that in some cases leads to synthetically useful products. Thus, 1,2-diarylcyclopropanes [240-243] as well as 2,3-diaryloxirans [244-246] and -aziridines (in the last case, also 2-monophenyl derivatives) [247,248] are cleaved upon photoinduced electron transfer sensitization. The final result, after back electron transfer, is trans-cis isomerization of the ring. In the presence of a suitable trap, however, a cycloaddition reaction takes place, involving either the radical cation or the ylide. Thus, dioxoles, ozonides or azodioxoles, respectively, are formed in the presence of oxygen and oxazolidines have been obtained from cyclopropanes in the presence of nitrogen oxide (Sch. 23). 

Miscellaneous Reactions. In two comprehensive publications, Taylor and co-workers detail the reactions of 1,2-dioxines with stabilised ylides as a route to diastereomerically pure cyclopropanes (Scheme 18). The reaction of ozonides with stabilised ylides produces a,p-unsaturated carbonyl compounds (Scheme 19). The E/Z isomeric ratio of the final products is affected by the identity and position of heteroatom substituents on the ozonide heterocycle. ... 

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