Ozonolysis of cycloalkenes

Despite earlier observations,624 625 ozonolysis of cyclic olefins in MeOH or in mixed solvents (ethers or esters and MeOH) followed by isomerization in the presence of Lindlar Pd and hydrogen does not give directly dicarboxylic acids. Instead, mainly the corresponding dialdehydes are formed.626 The best method of synthesis of dicarboxylic acids is ozonolysis of cycloalkenes in a mixture of acetic acid and formic acid followed by further oxidation with oxygen 626... 

Ozonolysis of cycloalkenes.b Cycloalkenes are converted by ozonation in the presence of an alcohol (usually methanol) into an acyclic product with an aldehyde group and an a-alkoxy hydroperoxide group at the terminal positions. The products are usually difficult to purify, but they can be converted into useful products that retain differentiated terminal functionality. 

Gao, S., Keywood, M., Ng, N.L., Surratt, J., Varutbangkul, V., Bahreini, R., Flagan, R.,C., and Seinfeld, J. H. (2004b) Low-molecular-weight and oligomeric components in secondary organic aerosol from the ozonolysis of cycloalkenes and a-pinene, J. Phys. Chem. A. 108, 10147-10164. 

The ozonolytic cleavage of cycloalkenes in the presence of methanol produces a chain with an aldehyde and a methoxy hydroperoxide group at the termini.8 The unsymmetrical ozonolysis product is manipulated in several... 

The ozonolysis of cyclohexene to 1,6-dioxygenated compounds is shown in Figure 17.28. Other cycloalkenes similarly afford other l,y-dioxygenated cleavage products. With the three methods for workup (Figure 17.27), this ozonolysis provides access to 1,6-hexanediol, 1,6-hexanedial, or to 1,6-hexanedicarboxylic acid. Each of these compounds contains two functional groups of the same kind. 

Cleavage products of cycloalkenes and cydoalkynes also reveal the cyclic structure. Ozonolysis of cyclohexene, for example, does not break the molecule into two aldehydes of lower carbon number, but simply into a single six-carbon compound containing two aldehyde groups. 

The ozonolytic cleavage of cycloalkenes in the presence of methanol produces a chain with an aldehyde and a methoxy hydroperoxide group at the termini. The unsymmetrical ozonolysis product is manipulated in several ways. Dehydration of the methoxy hydroperoxide group affords an ester (Procedure B). Alternatively, the aldehyde moiety is protected as an acetal. Under these conditions, the methoxy hydroperoxide is reduced (Procedure A) or dehydrated (Procedure C). 

The yield of OH radicals in the ozonolysis of a number of cycloalkenes has been determined by scavenging OH with cyclohexane (Sidebottom). The derived OH yield of about 40 % was found to be similar to that of cw-2-butene, providing support for the suggestion that OH yields from ozone-alkene reactions depend... 

There are three main transformations of the functional group interconversion (FGI), elimination (FGE) and addition (FGA), assigned by double arrows (Table 1.1). Another important retrosynthetic tool represents reconnection (RCN) of acyclic to cyclic structures. Reversal to a synthetic direction is the formation of an acyclic structure by ring opening. A typical example is reconnection of an a, co-dicarbonyl compound to cycloalkene, e.g., 1,6-hexanedialdehyde to cyclohexene. In the synthetic direction ozonolysis of the double bond in cyclohexene affords 1,6-dialdehyde. 

A similar mechanism has been postulated for reactions involving cycloalkenes. It has been shown that a copolymer of cyclooctene and cyclopentene (labelled on its double bond with is predominantly labelled in the C5 fragment, this result being obtained by reductive ozonolysis of the polymer [9j. The radioactivity found in the C5 diol proves that ring opening polymerization also proceeds via scission on the double bonds rather than cleavage of carbon—carbon single bonds. 

Further variations make ozonolysis a versatile tool in organic synthesis. Equations (9.116)—(9.118) illustrate the possibility of preparing terminally differentiated products from cycloalkenes 629 630... 

Given an alkene or cycloalkene (or diene, and so on), write the structures of the expected ozonolysis products. 

The oxidation of alkenes and cycloalkenes and their halogen derivatives with at least one hydrogen or halogen atom at the double bond leads to carboxylic acids. Ozonolysis usually requires the oxidative decomposition of the ozonide. The oxygen content of the ozonide is not sufficient for the formation of two molecules of acids or one dicarboxylic acid. The nonoxidative decomposition of cyclohexene ozonide gives an aldehyde-acid or its derivatives [1108]. It comes, therefore, as a surprise that carboxylic acids are claimed as products of the decomposition of ozonides by hydrogenation over the Lindlar catalyst [55] (equation 108). 

Additional terminal functionalization can be accomplished by several methods. Schreiber has developed general ozonolysis and workup procedures which enable a variety of products to be prepared from cycloalkenes (eq 3). Also, iron or copper salts can be... 

The cycloalkenes ozonolysis in the presence of methyl pymvate results in tri-substituted ozonides formation. The latter contain three reaction centers (peroxides, proton on the ozonides cycle and methoxy-carbonyl group) accessible for various functionalization. The cyclohexene ozonolysis in the presence of methylpyrovate gives ozonide whose treatment with PPhj or EtjN yields CHO(CHj) CHO and CHO(CH3),COOMe (after esterification), respectively. This method proved to be very convenient and practical way for the synthesis of linear compounds containing various ter-... 

Now we must find a way to convert the starting cycloalkene into the diol shown above. This can be achieved in just two steps. First, the ring is opened with an ozonolysis reaction to produce a dialdehyde. Then, the dialdehyde is reduced to a diol upon treatment with two equivalents of a reducing agent. Acetal formation then gives the final product. 

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