Esters from ozonides

Expls may be classified both from the chemical point of view and according to their uses. From the chemical viewpoint we distinguish between chemical individual substances and mixts. The former are divided into (1) nitro compds, (2) nitric esters, (3) nitramines, (4) derivatives of chloric and perchloric acids, (5) azides, and (6) various compds capable of pro-during an expln, for example fulminates, acetyl-ides, nitrogen rich compds such as tetrazene, peroxides and ozonides, etc... 

Due to the retractive forces in stretched mbber, the aldehyde and zwitterion fragments are separated at the molecular-relaxation rate. Therefore, the ozonides and peroxides form at sites remote from the initial cleavage, and underlying mbber chains are exposed to ozone. These unstable ozonides and polymeric peroxides cleave to a variety of oxygenated products, such as acids, esters, ketones, and aldehydes, and also expose new mbber chains to the effects of ozone. The net result is that when mbber chains are cleaved, they retract in the direction of the stress and expose underlying unsaturation. Continuation of this process results in the formation of the characteristic ozone cracks. It should be noted that in the case of butadiene mbbers a small amount of cross-linking occurs during ozonation. This is considered to be due to the reaction between the biradical of the carbonyl oxide and the double bonds of the butadiene mbber [47]. 

Catalytic oxidation of ozonides over platinum appears to be accompanied by the same ester by-product disadvantage found in the thermal process. Chain degradation by other reactions is less serious, however, and transesterification does not occur. The method can therefore be used to prepare a half-ester of a dicarboxylic acid from an ester of a suitable unsaturated acid. If ozonide autoxidation occurs by the route, ozonide — aldehyde — peracid, with the latter acting as precursor of both acid and ester products (20-24), it is interesting to compare reaction rates observed in the present study with the rate of uptake of oxygen by... 

For reducing ozonides or sterically hindered peroxides, magnesium and methanol proved to be a better and mild reducing agent <2004JOC2851>. Thus, the bicylic ozonide prepared from 1-phenylcyclopentene, which is prone to base-mediated cleavage, was cleanly reduced by Mg/MeOH to the keto-acid with the ketonic methyl ester as a by-product, whereas reduction with zinc and acetic acid affords mainly the keto-aldehyde with the keto-acid as a by-product (Equation 7). 

The ozonation of Feist s ester yields three products 2,3-dicarbomethoxytetrahydrofuran-4-one (III), 3,4-dicarbome-thoxy-5-hydroxy-2-oxa-2,3-dihydropyran (IV), and 4,5-di-carbomethoxy-l-oxaspiro[2.2 pentane (V). Structures were assigned primarily through spectroscopic evidence (mass, NMR, and infrared spectra). The last of these compounds is probably not a direct ozonation product (stoichiometry and trapping studies). A mechanism is proposed in which the initial step is formation of a primary ozonide. From that stage, the breakdown is abnormal. 

For future labeling syntheses of potential biosynthetic precursors, as well as for preparation of monocyclic diketones 70, on a 100- to 1000-g scale, additional, nonbiomimetic syntheses to these important intermediates were elaborated (63) (see Scheme 14). The key step of the first synthesis was oxidative cleavage of suitably substituted dimethyl indenes 68, either directly with permanganate-periodate or via remarkably stable ozonides 69. The required indenes 68 could be prepared from esters 67, and thus from very cheap educts like methacrylic acid and... 

In the ozonolysis of 1,3-dienes, one double bond often can be cleaved selectively, and in 1,3-cyclodienes, the regioselectivity in fragmentation of the primary ozonide depends upon the size of the rings (eq 13). Eq 13 shows that as the ring size contracts from cyclooctadiene to cyclohexadiene, the a,/3-unsaturated ester becomes favored over the enal. 

A variety of thioketones have found applicability in the synthesis of heterocyclic compounds. Chloro-thioacetone reacted with trialkoxy-phosphines to give thiirans. Thiophens have been prepared from mono-thio-j3-diketones, j8-thioketo-esters, > and from a-thioketo-acids. a-Thioacyl-y-lactones and -thiolactones rearrange in acid alcoholic solution to give dihydrofurans and dihydrothiophens, respectively. The simultaneous action of carbon disulphide, sulphur, and triethylamine on aliphatic thioketones gave mixtures of l,2-dithiole-3-thiones and 1,3-dithiole-2-thiones. The formation of thio-ozonides (1,2,4-trithiolans) by... 

It has been possible to show with the help of adsorption TLC, that isomers are formed when the methyl esters of unsaturated fatty acids are ozonised each of the isomers from methyl oleate has been isolated in a pure state [175]. Compounds which are not easily fractionated by argentation TLC, like as-methyl octadecenoate (methyl oleate) and mw5- mw5-methyl octadecadienoate (trans-trans methyl hnoleate ) or the corresponding triglycerides, have been separated as their ozonides [170]. This method is suitable, however, only for lipids with up to four double bonds. Ozone reacts with more highly unsaturated compounds to form short chain ozonides and undelfined side products [170]. 

Qeavage of ozonide 64 leads to the formation of long-chain aldehyde acetic acid 1-formyl-hexyl ester (65) and carbonyl oxide 66. Ester 65 was formed almost exclusively, which was attributed to the presence of an acetoxy group in vicinity of the olefinic double bond that might protect the aldehyde from a fast reaction with the carbonyl oxide to the secondary ozonide acetic acid l-[l,2,4]trioxalane-3-yl-hexyl ester (67). However, at higher olefin conversion the selectivity to aldehyde 65 decreases due to the increasing formation of secondary ozonide 67 and side reactions of aldehyde 65. 

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