Oxidative cleavage with aromatic rings

Under similar experimental conditions, the oxidation products of unsaturated compounds with an activated double bond by aromatic substitutent results essentially in cleavage of the double bond with formation of the corresponding carbonyl compounds. However, addition of oxygen leading to epoxide as secondary minor product is observed. In all cases, no oxidation of the aromatic ring is detected (Table 3). 

Tetracyanoethylene oxide [3189-43-3] (8), oxiranetetracarbonitnle, is the most notable member of the class of oxacyanocarbons (57). It is made by treating TCNE with hydrogen peroxide in acetonitrile. In reactions unprecedented for olefin oxides, it adds to olefins to form 2,2,5,5-tetracyanotetrahydrofuran [3041-31-4] in the case of ethylene, acetylenes, and aromatic hydrocarbons via cleavage of the ring C—C bond. The benzene adduct (9) is 3t ,7t -dihydro-l,l,3,3-phthalantetracarbonitrile [3041-36-9], C22HgN O. 

Hydroxyl elimination is necessary for the formation of benzaldehyde and benzoic acid derivatives and, ultimately, benzene and toluene (Fig. 7.46).2 It is proposed that a cleavage between the hydroxyl group and aromatic ring leads to benzenoid species which undergo further cleavage coupled with oxidation to give various decomposition products. 

Although this method is quite old it has stood the test of time, and is the basis of many modem oxidations with RuO. Sharpless used it for oxidations of alcohols, ethers, aromatic rings and for aUcene cleavage, so clearly it has a high range of applicability. 

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