OZONOLYSIS REACTION

Ozonolysis

Criegee Mechanism

Ozonolysis allows the cleavage of alkene double bonds by reaction with ozone. Depending on the work up, different products may be isolated: reductive work-up gives either alcohols or carbonyl compounds, while oxidative work-up leads to carboxylic acids or ketones.

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Mechanism of Ozonolysis

The mechanism was suggested by Criegee (Angew. Chem. Int. Ed., 1975, 87, 745. DOI) and has been recently revisited using ¹⁷O-NMR Spectroscopy by the Berger Group (Eur. J. Org. Chem., 1998, 1625. DOI).

First step is a 1,3-dipolar cycloaddition of ozone to the alkene leading to the primary ozonide (molozonide, 1,2,3-trioxolane, or Criegee intermediate) which decomposes to give a carbonyl oxide and a carbonyl compound:

The carbonyl oxides are similar to ozone in being 1,3-dipolar compounds, and undergo 1,3-dipolar cycloaddition to the carbonyl compounds with the reverse regiochemistry, leading to a mixture of three possible secondary ozonides (1,2,4-trioxolanes):

secondary ozonides are more stable than primary ozonides. Even if the peroxy bridge is shielded by steric demanding groups leading to isolable products, they should not be isolated from an unmodified ozonolysis, because still more explosive side products (tetroxanes) may have been formed:

As endoperoxides are investigated as antimalarial compounds, more selective methods have been developed for their preparation (for example the Griesbaum Coozonolysis). 

The Criegee mechanism is valid for reactions in hydrocarbons, CH₂Cl₂, or other non-interactive solvents. Alcohols react with the carbonyl oxide to give hydroperoxy hemiacetals:

The synthetic value lies in the way the complex mixtures of intermediates can be worked up to give a defined composition of products and a clean conversion of all peroxide species. The three main possibilities are given above, along with examples for the reagents used.

Recent Literature

Pyridine Is an Organocatalyst for the Reductive Ozonolysis of Alkenes

Ozonolysis in Solvent/Water Mixtures: Direct Conversion of Alkenes to Aldehydes and Ketones

One-Pot Oxidative Cleavage of Olefins to Synthesize Carboxylic Acids by a Telescoped Ozonolysis-Oxidation Process

Unsymmetrical Ozonolysis of a Diels-Alder Adduct: Practical Preparation of a Key Intermediate for Heme Total Synthesis

Catalytic Asymmetric Reductive Coupling of Alkynes and Aldehydes: Enantioselective Synthesis of Allylic Alcohols and α-Hydroxy Ketones

N-Tosyl-3-halo-3-butenylamines underwent efficient Ullmann-type coupling to afford 2-alkylideneazetidines, which could be readily converted to the corresponding β-lactams by oxidation with O₃.