Ozonolysis reaction with butenes

The ozonolysis reaction, followed by reductive workup with sulfur dioxide, as described in Part A of the present procedure, illustrates a general method which has been developed for the preparation of acetals. Application of the procedure is illustrated by conversion of the following olefins in alcoholic solution to the corresponding acetals (1) l-chloro-4-(o-nitrophenyl)-2-butene to o-nitrophenylacetaldehyde dimethyl acetal in 84% yield (2) l,4-dibromo-2-butene tobromoacetaldehyde dimethyl acetal in 67% yield (3) 3-butenoic acid to malonaldehydic acid diethyl acetal ethyl ester in 61% yield (4) cyclopentadiene to malonaldehyde bis(diethyl acetal) in 48% yield and (5)... 

The nature and the distribution (Table II) of the ozonolysis products in conjunction with the probable modes of their formation allow also a qualitative rationalization of the observed ozone-olefin stoichiometry. Three reactions compete with ozone for the starting material, trans-2,3-dibromo-2-butene. These reactions are the formation of 3,3-dibromobutanone, 31, and the formation of the brominated products, 34 and 35. On the other hand, hydrogen bromide is oxidized to form bromine and water, which consumes ozone on top of the regular olefin— ozonolysis reaction. An attempt to explain the observed stoichiometry quantitatively did, however, not lead to a satisfactory correlation between the actual ozone consumption and the observed material balance. This... 

The overall mechanisms for reaction of O3 and NO3 with 2-buten-l-ol are similar to those with 2-propen-l-ol described previously. O3 will add to the C=C bond resulting in formation of a trioxide which decomposes to form two carbonyl compounds and two biradicals. Grosjean and Grosjean (1995) reported acetaldehyde and glycolaldehyde as major products from the ozonolysis of 2-buten-l-ol with formation yields of (64 6)% and (79 18)%, respectively. Formaldehyde was also observed as a product (23 7)%, its formation involves the reactions of biradicals (CH3CHOO and HOCH2COO). 

A total synthesis of ( )-aromatin has utilized the lithium anion of the dithiane of (E)-2-methyl-2-butenal as a functional equivalent of the thermodynamic enolate of methyl ethyl ketone in an aprotic Michael addition (Scheme 189) (81JOC825). Reaction of the lithium anion (805) with 2-methyl-2-cyclopentenone followed by alkylation of the ketone enolate as its copper salt with allyl bromide delivered (807). Ozonolysis afforded a tricarbonyl which cyclized with alkali to the aldol product (808). Additional steps utilizing conventional chemistry converted (808) into ( )-aromatin (809). 

As it is well known, acyloxy, alkoxy, or phenoxy groups connected to sp2-hybridized carbon atoms in alkenes or aromatics are unreactive to nucleophilic substitution. However, after alkene ozonolysis such groups become attached to sp3-hybridized carbon atoms and become reactive. It was shown <1989TL1511> that such substitutions have to be carried out at 40 °C when they compete with thermolytic reactions of the ozonides, lowering the yields. However, if 2,3-dichloropropene and as- or /ra/rt-1,2,4-trichloro-2-butene are ozonized, one obtains stable ozonides 68a-70... 

Ozonolysis of truns-2,3 -Dibromo-2-butene in Inert Solvents. Starting Material. The title compound 23 was prepared by adding bromine to 2-butyne at ca. —30° to —40°C. The reaction produced 23 in more than 95% yield, along with less than 5% of the cis-isomer, 24, and trace amounts of as yet unidentified by-products. 

Another potential dark source of in the atmosphere, more particularly in the boundary layer, is from the reactions between ozone and alkenes. The ozonolysis of alkenes can lead to the direct production of the OH radical at varying yields (between 7 and 100%) depending on the structure of the alkene, normally accompanied by the co-production of an (organic) peroxy radical. As compared to both the reactions of OH and NO3 with alkenes the initial rate of the reaction of ozone with an alkene is relatively slow, this can be olfset under regimes where there are high concentrations of alkenes and/or ozone. For example, under typical rural conditions the atmospheric lifetimes for the reaction of ethene with OH, O3 and NO3 are 20 h, 9.7 days and 5.2 months, respectively in contrast, for the same reactants with 2-methyl-2-butene the atmospheric lifetimes are 2.0 h, 0.9 h and 0.09 h. 

Although a-dicarbonyl compounds are not known to be products of the ozonolysis of olefins, biacetyl has been isolated in photochemically initiated reactions 14, 15) which result in the net oxidation of olefins in the gas phase. For example, when a mixture of ci5-2-butene, nitric oxide, and air is irradiated, small amounts of biacetyl are isolated. One of the pathways suggested to explain the production of biacetyl involves the reaction of ozone with ci5-2-butene (14) ... 

Dimethyl-1-butene will not yield a methyl carbonyl compound upon ozonolysis with reductive workup. Hence, it will subsequently not give a positive iodoform reaction. 

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... 

If the focus is on the C=C unit of 2,3-dimethyl-2-butene, the dipolar addition reaction cleaves the first bond (the n-bond), and the rearrangement of the 1,2,3-trioxolane to the 1,2,4-trioxolane cleaves the second bond (the c-bond). The conversion of an alkene to an ozonide is known as ozonolysis, and it is an example of an oxidative cleavage reaction. The ozonide is usually not isolated, but a second chemical step is performed in the same flask. When treated with hydrogen peroxide, the products of this reaction are 2-propanone (acetone) and a second molecule of acetone. This statement is phrased this way because an unsymmetrical alkene will give two different ketones. In effect, the C=C unit is cleaved and each carbon is oxidized to a C=0 unit. The mechanism described for this reaction is consistent with known chemistry of ketones and aldehydes and other carbonyl-bearing functional groups. A full discussion of carbonyl chemistry will be presented in Chapters 17 and 19. 

The application of ozone is a new and convenient way for the preparation of cyanoacetylaldehyde (3-oxopropylonitrile) (1) and its stable dimethyl acetal (3,3-dimethoxypropylonitrile) (2) used as valuable intermediates for organic synthesis [72]. For this purpose the ozonolysis of (E)-l,4-dicyano-2-butene or 3-butylonitrile is carried out. Then the oxidates are treated by DMS yielding 1. Further, compound 1 can be used either directly in the next reactions or is transformed into 2. The 2 output amounts to from 67 to 71%. The acetal can be again hydrolyzed to 1 by treatment with ion-exchange resin Amberlyst-15 [72]. 

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