Ozonolysis of alkenes, and

In addition to the ozonolysis of alkenes and a few aromatic compounds [93, 104], ozone oxidizes other groups. Thus saturated hydrocarbons containing tertiary hydrogen atoms are converted into tertiary alcohols [105, 106], and some alkenes are transformed into epoxides [107] or a,p-unsat-urated ketones [108], Benzene rings are oxidized to carboxylic groups [109, ethers [110] and aldehyde acetals [111] to esters aldehydes to peroxy acids [772] sulfides to sulfoxides and sulfones [775] phosphines and phosphites to phosphine oxides and phosphates, respectively [775] and organomer-cury compounds to ketones or carboxylic acids [114]. 

The functional group transform for ozonolysis of alkenes and all oxidative cleavage reactions of alkenes can be summarized by... 

Gas-Phase Ozonolysis of Alkenes and the Role of the Criegee Intermediate... 

The Criegee intermediate has been claimed to be of importance in tropospheric chemistry [4] but never been observed by direct spectroscopic methods in the ozonolysis reaction. The aims of our research were therefore (i) to provide spectroscopic (IR, UVA is) data of a variety of substituted carbonyl O oxides, (ii) to develop a theoretical model which allows the prediction of the spectra of carbonyl O oxides which are not accessible by laboratory studies, but might be of importance to tropospheric chemistry, and (iii) to elucidate the mechanism of the ozonolysis of alkenes and investigate the role of carbonyl O oxides in these reactions. 

Ozonolysis has both synthetic and analytical applications m organic chemistry In synthesis ozonolysis of alkenes provides a method for the preparation of aldehydes and ketones... 

Ozonolysis of alkene 446 in the presence of acetaldehyde afforded diketone 448 through the intermediacy of 447. Ring expansion through Beckmann rearrangement took place when bis-oxime 449 was mesylated and warmed in aqueous tetrahydrofuran (THF). The bis-lactam so formed gave piperidinediol 450 on reduction with lithium aluminium hydride, and this compound was transformed into ( )-sparteine by treatment with triphenylphosphine, CCI4, and triethylamine (Scheme 105) <20050BC1557>. 

Acid-catalyzed dimerization and oligomerization of 1,2,4-trioxolanes will be covered in Section 4.16.5.2.1. In general, ozonides are not prone to spontaneous polymerization. Polymeric products can be obtained from the ozonolysis of alkenes but most likely arise from reaction of the primary ozonide. Bicyclic 1,2,4-trioxolanes such as 2,5-dimethylfuran endoperoxide can dimerize on warming in CCI4 (Section 4.16.5.1.1). 1,2,4-Trithiolane tends to polymerize at room temperature especially if left open to air, whilst more highly substituted ring systems are stable. 

The ozonolysis of alkenes has been comprehensively covered in several excellent reviews (see Section 4.16.1) and will therefore not be discussed in detail here. It is pertinent, given the importance of 1,2,4-trioxolane synthesis, to highlight the key points of the ozonolysis reaction mechanism and several other developments. 

Ozonolysis of alkenes on solid supports, notably polyethylene <85JA5309>, has greatly increased the scope of the reaction in the preparation of 1,2,4-trioxolanes. Competing reactions of intermediates are avoided and the mild conditions often allow isolation of relatively unstable or previously unobtainable 1,2,4-trioxolanes. 

Schindler and coworkers verified the formation of hydroxyl radicals kinetically and further RRKM calculations by Cremer and coworkers placed the overall concept on a more quantitative basis by verifying the measured amount of OH radical. An extensive series of calculations on substituted alkenes placed this overall decomposition mechanism and the involvement of carbonyl oxides in the ozonolysis of alkenes on a firm theoretical basis. The prodnction of OH radicals in solution phase was also snggested on the basis of a series of DFT calculations . Interestingly, both experiment and theory support a concerted [4 4- 2] cycloaddition for the ozone-acetylene reaction rather than a nonconcerted reaction involving biradical intermediates . 

Gutbrod, R., R. N. Schindler, E. Kraka, and D. Cremer, "Formation of OH Radicals in the Gas Phase Ozonolysis of Alkenes The Unexpected Role of Carbonyl Oxides, Chem. Phys. Lett., 252, 221-229 (1996). 

Sauer, F., C. Schafer, P. Neeb, O. Horie, and G. K. Moortgat, Formation of Hydrogen Peroxide in the Ozonolysis of Isoprene and Simple Alkenes under Humid Conditions, Atmos. Enriron., 33, 229-24f (f999). 

Ozonolysis of alkenes (end of Section 6.4) and cleavage of glycols (Section 14.11) afford carbonyl compounds. These reactions, once used for structure determinations, have been superseded by spectral methods. 

Aldehydes and ketones are obtained by ozonolysis of alkenes (see Section 5.7.6) and hydration of alkynes (see Section 5.3.1). 

Carbon monoxide has been used to scavenge OH fonned from the ozonolysis of alkenes. The CO2 tints generated was detected by FTIR spectroscopy and the "OH yields for individual reactions were calculated.239 The significance of the OH-induced intramolecular transformation of glutathione thiyl radicals to a-aminoalkyl radicals has been discussed with respect to its biological implications.240 The kinetics and mechanism of the process indicated that it could be a significant pathway for the selfremoval of glutathione thiyl radicals in vivo. 

Ozonolysis of alkenes in the presence of amine A-oxides resulted in reductive ozonolysis, i.e, the direct formation of aldehydes in high yields, avoiding the generation and isolation of ozonides or other peroxide products. Use of DMSO and tertiary amines improved the yield of aldehydes but some amount of ozonides remained. This... 

Like aldehydes, ketones can be prepared in a number of ways. The following sections detail some of the more common preparation methods the oxidation of secondary alcohols, the hydration of alkynes, the ozonolysis of alkenes, Friedel-Crafts acylation, the use of lithium dialkylcuprates, and the use of a Grignard reagent. 

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). 

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>. 

An older paper <1971MI873> reported that ozonolysis of alkenes in the presence of tertiary amines resulted in the formation of aldehydes. A recent reinvestigation <20060L3199> has shown that amine oxides were responsible for this reductive ozonolysis . Indeed, pretreatment of the tertiary amines with ozone, giving rise to amine oxides, accounted for this phenomenon. A preparative method emerged, by treating the alkene (e.g., 1-decene) at 0 °C with a solution of 2% 03/02 in dichloromethane (2 equiv of ozone relative to the alkene) in the presence of an excess (about threefold molar excess) of A-methylmorpholine A-oxide, pyridine A-oxide, or l,4-diazabicyclo[2.2.2]octane A-oxide (DABCO A-oxide). Yields of aldehydes (nonanal in the above example) were 80-96%, and the excess of amine oxide ensured the absence of residual ozonide (Scheme 21). 

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). 

Dipolar Cycloadditions and 1,3-Dipolar Cycloreversions as Steps in the Ozonolysis of Alkenes... 

Fig. 17.27. Intermediates (center row) and final products (bottom row) of the ozonolysis of alkenes.

Horie and G. K. Moortgat, Gas-phase ozonolysis of alkenes. Recent advances in mechanistic investigations, Acc. Chem. Res 1998,31, 387-396. 

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