Cleavage of olefins

Ozonation ofAlkenes. The most common ozone reaction involves the cleavage of olefinic carbon—carbon double bonds. Electrophilic attack by ozone on carbon—carbon double bonds is concerted and stereospecific (54). The modified three-step Criegee mechanism involves a 1,3-dipolar cycloaddition of ozone to an olefinic double bond via a transitory TT-complex (3) to form an initial unstable ozonide, a 1,2,3-trioxolane or molozonide (4), where R is hydrogen or alkyl. The molozonide rearranges via a 1,3-cycloreversion to a carbonyl fragment (5) and a peroxidic dipolar ion or zwitterion (6). 

Oxidative cleavage of olefins is frequently a useful procedure synthetically as well as analytically. Ozonization is an effective means of carrying out such a cleavage under... 

Most of the preceding sections in this chapter have emphasized the use of CM for the homologation of terminal olefins. The microscopic reverse of this reaction, however, is also of great synthetic interest, as it provides a mild method for the cleavage of olefins. When ethylene gas is used as the cross-partner, the resulting CM reaction is known as ethenolysis. Prior to 2000, ethenolysis was almost exclusively used within the oleochemical industry to process unsaturated fatty oils or triglycerides into compounds of lower molecular weight. With the advent... 

Oxidative cleavage of olefins, terminal alkynes, or aromatic rings 9-11 Oxidation of aromatic side chains 9-21 Oxidation of amines 9-22 Oxidation of primary alcohols or ethers... 

While die above reactions will provide carboxylic acid products, each has problems associated with it. The cleavage of olefins to carboxylic acids [reaction (7.1)] can be carried out using potassium permanganate or by ozonolysis at low temperature followed by oxidative workup with hydrogen peroxide. Neither of diese mediods is very useful since only symmetric olefins provide a single carboxylic acid product. Unsymmetrical olefins give a mixture of two acids which must be separated. Furthermore the most useful synthetic processes are those which build up structures, whereas these reactions are degradative in nature. 

Homolytic autoxidations of hydrocarbons often give complex mixtures of products-the autoxidation of olefins is a prime example. There is a great incentive, therefore, to search for catalysts that can promote the selective oxidation of olefins by essentially nonradical mechanisms. For example, there is no method available for carrying out the selective epoxidation or oxidative cleavage of olefins (see Section III.C) by molecular oxygen. In order to be successful, any heterolytic pathway for the metal-catalyzed oxidation of a substrate must, of course, be considerably faster than the ubiquitous homolytic processes for autoxidation. Thus, the metal catalysts discussed in the following sections, in addition to being able to promote heterolytic oxidations, are also able to catalyze homolytic processes. 

There is considerable industrial interest in the direct epoxidation or oxidative cleavage of olefins with molecular oxygen by the following overall transformations ... 

Fig. 12 Mechanism of Ru04-mediated oxidative cleavage of olefins...

Oxidative cleavage of carbon-carbon double bonds or v/c-diols can lead to aldehydes, ketones or carboxylic acids depending upon the conditions employed. Oxidative cleavage of olefins is important from the viewpoint of... 

Figure 3.31 Catalytic cycle of the ruthenium-catalysed cleavage of olefins in the presence of percarboxylic acids.

Figure 3.32 Cleavage of olefins with hydrogen peroxide/ vanadium ( V) systems.

Figure 3.33 Catalytic cleavage of olefins using a mixed ruthenium (If )/molybdenum (VI)/hydrogen peroxide system.

Table 3.4 Cleavage of olefins using a Ru(III)/Mo(VI)/hydrogen peroxide systema...

Hydrogen peroxide with Milas reagent is also suitable for the cleavage of olefins. The system has been used to prepare aromatic aldehydes such as anisaldehyde from anethole, pipernal from isosafrole and vanilin from iso-eugenol.170,171 Hydrogen peroxide and chromium(III) can be used to cleave methyl methacrylate to methyl pyruvate.172... 

Heterogeneous systems have also been developed for the cleavage of olefins with hydrogen peroxide.174,175 Titanium-containing zeolites can be used to cleave olefins.176 Adam and co-workers have recently shown that acetophenone, an oxidation product from the Ti-zeolite catalysed oxidation of a-methyl-styrene, derives from 2-hydroxyperoxy-2-phenylpropan-l-ol as an intermediate (which they detected and isolated) (Figure 3.34).177... 

Fig. 4.34 A catalytic cycle for ruthenium-catalyzed oxidative cleavage of olefins.

The tandem 0s04-catalyzed oxidative cleavage of olefin 269 with Oxone as the co-oxidant and sequential direct oxidation of intermediate aldehyde in alcoholic media led to cyclic keto lactone 270 in 45% yield (Equation 34) <20030L3089>. Similar oxidative cyclization with KMnCT-GuSITr resulted in 32% yield of 270 <1994T11709>. 

Though the cleavage of olefins with ozone has been carried out for some 60 years on the basis of publications by Harries82 only a relatively small number of definite ozonides have been isolated and described. Criegee et al,96 have published a table of definite ozonides. Reviews of the field have been published by Rieche,2,19 Long,97 and Criegee,4 and the lectures of the International Ozone Conference 98 have also been published. 

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