Reactions of ozonides. VIII. An examination of the possibility of reversible ozonide formation using ¹⁴C labelling

Abstract

Carboxyl-14G-10-formyldecanoic acid was made by 14C02 carbonation of 10-undecenylmagnesium bromide and ozonolysis of the product. Attempts were made to equilibrate its methyl ester with CHz / \ @R(CM2)gCOOMe and CH2 GH(CH2)8COOMe in various solvents. Little in-'0-0' corporation of label in the re-isolated ozonide was found, and it was concluded that under normal ozonolysis conditions the formation of ring ozonide is essentially irreversible. Slight incorporation in chloroform is explicable either by reversal of the Criegee n~echanism of ozonide formation or by reversal of the recently suggested regenerative carbonyl -primary ozonide reactions.Canadian Journal of Chemistry, 47, 43 (1969) A recent interest in the mechanism of formation of ozonides from oiefins has been sparled by a close examillation of the stereochemistry of the reaction. The Criegee mechanism (I) accommodates stereospecificity by invoking a solvent cage which must be penetrated in crossozonide formation (2). To explain different cis-trans ozonide ratios in cross ozonides from cis and trans olefins, a mechanism has been proposed involving a carbonyl -primary ozoilide interaction step (3). Recently, refinements have been added to the Criegee n~echanisrn by advocating the formation of syn and arzti zwitterions which combine stereospecifically with aldehydes or ketones io yield ozonides (4).Two schoois have studled ozonide r i~~g formation using isotopic oxygen (36,5,6). Incorporation of the label nil both the ether and peroxid~c oxygens or aliphatic ozo~iides was interpreted to mean simultaneous operation of the Criegee mechanism and a regenerative carbonyl -primary ozonide interaction as shown :In the aromatic 180 study, peroxide irtcorporatlon was very nearly negligible and the label it was pointed out that the same seven-membered appeared in the ether oxygen. This silpports the intermediate can give ether-labelled ozonide by Criegee mechanism, but does not exciude a C-O fi$sion of the primary ozonide as shown interactions of the type shown above, because below rather than 0-0 fission as shown above:Can. J. Chem. Downloaded from www.nrcresearchpress.com by 34.217.195.47 on 05/12/18For personal use only.