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26.1.2.2.3 Variation 3: By Ozonolysis

DOI: 10.1055/sos-SD-026-00062

Balaban, T. S.Science of Synthesis, (200526135.

Ozonolysis has been applied as a tool to determine the position of C=C bonds in unsaturated compounds. Ozone adds to C=C bonds to form very reactive ozonides which in some cases can be isolated. The ozonides are subsequently cleaved by hydrolysis under either reductive or oxidative conditions. For the synthesis of ketones the C=C bond must be at least trisubstituted, of which terminal alkenes are the most reactive, or tetrasubstituted. Mechanistically the reaction has been intensively studied by Criegee and co-workers and has been reviewed.[‌66‌,‌67‌] The proposed mechanism is shown in Scheme 13. The initial addition product has been isolated as a crystalline material from the reaction of ozone with (E)-2,2,5,5-tetramethylhex-3-ene,[‌68‌] and could be reduced to the racemic diol proving that one CC bond is still intact after the ozone addition which must occur in a cis fashion. This highly unstable adduct cleaves to a carbonyl oxide, which can be formulated as a zwitterionic species, and to a carbonyl compound. These can recombine in a different way to form the ozonide. Alternatively, the zwitterion, which can also be formulated as a 1,3-diradical, can dimerize to the bisperoxide or oligomerize.

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