Ozone, reaction + nitrones

Many combinations of atoms are conceivable, among them azides, nitrones, nitrile oxides, and ozone. As these systems have four tt electrons, they are analogous to dienes, and cycloadditions with alkenes and alkynes are allowed [4 + 2] reactions. These are discussed in Section 10.3. 

Some preliminary kinetic work has been reported on the ozonolysis of nitrones. Ozone has been established as an electrophile towards carbon-carbon unsaturated systems in its reaction with some p-substituted-N-phenylbenzaldoximes in chloroform at —60°C the order of reactivity p-OMe > H > p-Cl has been established . Such a sequence could be accommodated by a process such as... 

Ozone has been used to cleave nitronate anions, resulting in the high yield production of either aldehydes or ketones. An example of this reaction is shown in eq 35. This is a very general method and has advantages over the Nef reaction which requires strong acid conditions, and other procedures utilizing permanganate or Titanium(III) Chloride. 

In addition to tin and silicon, carbon-nitrogen double bonds as hydrazones, oximes, and nitrones can be treated with ozone to form carbonyl compounds (eq 53)7 While the transformation can be accomplished on several types of substrates, ketone-derived starting materials (e.g., ketoximes) perform better in the reaction, as the aldehyde-derived starting materials have the potential for overoxidation to the corresponding carboxylic acid product. 

When ozone is passed through n-heptylamine that is adsorbed on neutral silica gel, 1-nitroheptane is formed in 70% yield. This in turn may be converted into n-heptaldehyde by a new modification of the Nef reaction in which the nitroheptane is adsorbed on to basic alumina, and the heptaldehyde eluted with ether 48 hours later A complementary method involves the oxidative cleavage of nitronate anions under very mild conditions using t-butyl hydroperoxide and a vanadium catalyst. This method was exploited to provide an improved route to the prostaglandin intermediate anri-7-(diethoxymethyl)-5-norbornen-2-one (8) (Scheme 25). 

Nowadays a broad range of different 1,3-dipoles, ozone, azides ° and diazoalkanes on the one hand as well as dipoles like nitrones, nitro compounds, carbonyl ylides, nitrile oxides, nitrile imines and ylides on the other hand, are well-established. The addition of these 1,3-dipoles to an alkene is one of the most frequently used cycloaddition reactions in organic synthesis. ... 

The ozonation mechanism for the iV-iV -diaryl-p-phenylenediamine antiozonants is identical to the above described mechanism except that the reaction terminates with the formation of the nitrone and the release of oxygen after reacting with the ozone, Step (3) [4]. 

The most common antiozonant from the class, Af-A -dialkyl-p-phenylenediamine, is Af,Af -bis-(l,4-dimethylpentyl)-p-phenylenediamine (77PD), and the ozonation mechanism reported in the literature for this class of antiozonant is shown on the following page in a simplified form, and is similar to the one reported for the A -alkyl-A -aryl-p-phenylenediamine up to the point where the second mole of ozone reacts with the reaction product previously formed and yields the nitrone. Step (3), which can react further with more ozone to form the dinitrone compound. Step (4) [5]. 

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