Secondary ozonide alkene

Ozonolysis of alkenes in participating solvents such as alcohols often leads to trapping of intermediates. Most commonly, an alcohol will react with the carbonyl oxide zwitterion, generated from cycloreversion of the primary ozonide (Section 4.16.8.2), to give an alkoxy hydroperoxide. The secondary ozonide (1,2,4-trioxolane) is usually more stable to nucleophilic attack from alcohols. 

In any event, in the solvent cage in which they are formed in the liquid phase, or for higher molecular weight alkenes condensed on surfaces, the two fragments formed by decomposition of the primary ozonide are held in close proximity and recombine to form a secondary ozonide ... 

Ozonolysis of cyclic olefins in the presence of carbonyl compounds gives the corresponding cross-ozonides.1329 In the ozonation of 1,2,4,5-tetramethyl-1,4-cyclohexadiene, oxidative dehydrogenation (formation of 1,2,4,5-tetramethylben-zene) was found to compete with oxidative cleavage because of steric hindrance.1330 Secondary ozonides (the 76 1,2,4-trioxolanes) are formed in high yields in the gas-phase, low-temperature ozonation of terminal and disubstituted alkenes.1331... 

A thorough theoretical analysis of the Criegee mechanism for the ozonolysis of cis- and trans-symmetrical alkenes Rl IG—Cl IR has been performed by semiempirical AMI calculations <1997JOC2757>. The experimentally observed stereoselectivity for bulky groups (e.g., R = Bu ) is that from the m-alkene a cisltrans ratio of 7 3 is encountered while from a trans-alkene a 3 7 ratio for the cisltrans secondary ozonides resulted. With smaller R groups (e.g., R = Me) both as- and trans-alkenes lead preferentially to the trans secondary ozonide (Scheme 1). 

While both the primary and secondary ozonides have been isolated and characterized, the pair formed by the carbonyl oxide (CO) and the carbonyl compound (CC) has never been directly put into evidence. This elusive intermediate, called also Criegee intermediate zwitterion (CZ), according to this AMI study which did not take into account solvent effects, forms a tight pair or a dipolar complex (DC). The primary ozonide has an O-envelope halfchair conformation and as such two conformers are possible from a rfr-alkene 11 and 12 and only one 13 from the trans-alkene. The splitting of the primary ozonide can lead either to an anti 14 or syn 15 CO and has a determining role for the stereochemical outcome of the reaction <1997JOC2757>. 

Three methods were used for making tri- or tetra-substituted 1,2,4-trioxolanes in the investigations of the reaction between these secondary ozonides and Lewis acids co-ozonolysis of oximes and ketones (method A), co-ozonolysis of enol ethers and ketones (method B), and ozonolysis of alkenes (method C, Scheme 10 and Table 5) <2000J(P1)3006>. 

The mechanism proposed by Criegee for the ozonolysis of alkenes <1975AGE745> considers an initial it-complex between the alkene and ozone which decays via a 1,3-dipolar cycloaddition into a 1,2,3-trioxolane or primary ozonide, known also as the molozonide . These compounds are unstable, even at low temperatures, and due to cycloreversion decompose into a carbonyl fragment and a CO, which may recombine by another 1,3-dipolar cycloaddition step to form the more stable 1,2,4-trioxolane ( secondary ozonide or final ozonide (see also Section 6.06.2). 

Neeb, P, Horie, O. and Moortgat, G.K. (1996) Formation of secondary ozonides in the gas-phase ozonolysis of simple alkenes. Tetrahedron Letters, 37, 9297-9300. 

Preparation of Tertiary Amines from Alkenes and Secondary Amines. A useful preparation of tertiary amines from alkenes can be achieved when a secondary ozonide is treated with a secondary amine (eq 50) 7 The reaction is quite versatile and provides tertiary amines when the reaction is carried out at reflux after addition of the amine. When the reaction medium was kept at room temperature, isolation of the enamine was observed, making this a clean, four-step, one-pot preparation of morpholino enatnines and tertiary amines for use in s)uithesis. Overall, the reaction performed best with morpholine some problems were encountered with methylenecyclohexane and piperidine, as it seems the enamine intermediate is difficult to form in such a hindered system. 

Fig. 8.3 Ozonolysis allows the cleavage of alkene double bonds. According to the Criegee mechanism the primary ozonide (POZ) is rapidly transformed into the more stable secondary ozonide (SOZ). Depending on the work-up, different products may be isolated. Oxidative work-up with hydrogen peroxide leads to carboxylic acids/ketones, while reductive work-up with either dimethyl sulfide or sodium borohydride gives aldehydes/ketones or alcohols, respectively...

Ozone plays a major role in the degradation of unsaturated VOCs in the troposphere, especially during night-time. The rate constants of the ozonolysis of a variety of alkenes have been reported [1]. However, in most instances the fate of the primary products of the ozonolysis is unknown, although the secondary reaction products are of crucial importance for the overall understanding of the alkene/ozone chemistry. The classical Criegee mechanism of the ozonolysis reaction involves the primary ozonide (POZ, 1,2,3-trioxolane), which cleaves to the Criegee intermediate (carbonyl O oxide) and a carbonyl compound [2, 3]. The secondary ozonide (SOZ, 1,2,4-trioxolane) is formed from these components in a [l,3]-dipolar cycloaddition reaction. 

The main results of our investigations are (i) The first step in the alkene/ozone reaction is the formation of a 7i-complex with absorptions in the near UV or visible range, (ii) At 50-70 K this complex reacts to the primary ozonide (POZ) and, depending on substituents, traces of the secondary ozonide (SOZ). (iii) No carbonyl oxide was observed under any conditions used in our ozonolysis experiments, (iv) Some of the partially oxidized products formed are not in accordance with the Criegee mechanism and thus alternative mechanisms have to be considered. 

Mechanism of Ozonolysis (Criegee mechanism) The initial step of the reaction involves a 1,3-dipolar cycloaddition of ozone to the alkene leading to the formation of the primary ozonide (molozonide or 1,2,3-trioxolane), 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 compound with the reverse regio-chemistry, leading to a relatively stable secondary ozonide (1,2,4-trioxolane) (Scheme 5.47). 

Temperature-programmed thermal desorption particle beam MS of collected secondary aerosol particles shows that the major ozonization products of normal alkenes in an environmental chamber include organic hydroperoxides, peroxides, final ozonides and monocarboxylic acids. Attempts to analyze these compounds by GC result in their decomposition to simpler molecules". 

Substrates suitable for oxidative conversion into carbonyl compounds are alkenes, primary or secondary alcohols, and benzyl halides. Polystyrene-bound alkenes have been converted into aldehydes (with the loss of one carbon atom) by ozonolysis followed by reductive cleavage of the intermediate ozonide (Entry 1, Table 12.3). 

The first step, a 1,3-dipolar addition, results in the formation of a primary ozonide (1 equation 6). This intermediate then opens to give a carbonyl and a zwitterion that can recombine to give the more stable normal ozonide (2 equation 7). Reduction of (2), without isolation, by lithium aluminum hydride, diborane or sodium borohydride dten gives either primary or secondary alcohols, depending on the nature of starting alkene (equation 8). 

Tertiary amines. Using a secondary amine to decompose an ozonide derived from 1-alkene effects its alkylation. The amine initiates an eliminative fragmentation of the ozonide to generate an aldehyde and dialkylammonium formate. Schiff base formation from the aldehyde and another molecule of the amine is then followed by reduction by the formate ion. 

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