Alkenes reactions with carbon dioxide

Methylenecyclopropanes 9 with geminally disubstituted alkene moieties undergo palladium-catalyzed [3-1-2] cycloaddition reactions with carbon dioxide under pressure. Besides cycloadduct 10 arising from formal distal cleavage of the MCP, furan-2(5//)-one 11, resulting from double-bond isomerization, is formed in variable amounts, depending on the substrate as well as the specific catalyst used. ... 

Addition of anionic nucleophiles to alkenes and to heteronuclear double bond systems (C=0, C=S) also lies within the scope of this Section. Chloride and cyanide ions are effieient initiators of the polymerization and copolymerization of acrylonitrile in dipolar non-HBD solvents, as reported by Parker [6], Even some 1,3-dipolar cycloaddition reactions leading to heterocyclic compounds are often better carried out in dipolar non-HBD solvents in order to increase rates and yields [311], The rate of alkaline hydrolysis of ethyl and 4-nitrophenyl acetate in dimethyl sulfoxide/water mixtures increases with increasing dimethyl sulfoxide concentration due to the increased activity of the hydroxide ion. This is presumably caused by its reduced solvation in the dipolar non-HBD solvent [312, 313]. Dimethyl sulfoxide greatly accelerates the formation of oximes from carbonyl compounds and hydroxylamine, as shown for substituted 9-oxofluorenes [314]. Nucleophilic attack on carbon disulfide by cyanide ion is possible only in A,A-dimethylformamide [315]. The fluoride ion, dissolved as tetraalkylammo-nium fluoride in dipolar difluoromethane, even reacts with carbon dioxide to yield the fluorocarbonate ion, F-C02 [840]. 

The results of some oxidations with potassium permanganate differ depending on the pH of the reaction. For example, stearolic acid gives 9,10-diketostearic acid at pH 7-7.5 (achieved with carbon dioxide) and azelaic acid on treatment at pH 12 [864]. In some reactions, potassium permanganate is used as a catalyst for oxidation with other oxidants, such as sodium periodate. Thus alkenes are cleaved to carbonyl compounds or acids via vicinal diols obtained by hydroxylation with potassium permanganate, followed by cleavage by sodium periodate [763, 552]. 

In the field of olefin carboxylation, stoichiometric reactions have been described to occur between non-activated alkenes, CO2 and an electron-rich transition-metal complexes, such as Ni(0) [3], Ti(II) [4] or Fe(0) [5]. A Pd-catalyzed CO2 fixation occurs into methylenecyclopropane derivatives affording lactones [6]. The reaction of carbon dioxide with ethylene is difficult and its carboxylation to propionic acid, catalyzed by Rh derivatives [7], needs drastic experimental conditions. 

Trialkyl phosphorus ylides, R3P=CH2, are strong nucleophiles and react with organic ketones and aldehydes to form alkenes via a [2+2] cycloaddition mechanism (Wittig Reaction). We have discovered recently that such ylides can also react with free carbon dioxide at one atmosphere and room temperature. When Me3P=CH2 in THF was bubbled with carbon dioxide gas for 30 minutes, free ketene, CH2=C=0, was produced. The formed... 

When the vinyllithium intermediate (190) is treated with water, the procedure provides a useful synthetic method for the conversion of ketones to alkenes (Scheme 79). The method is illustrated by the conversions of the tosylhydrazones of phenyl isopropyl ketone (194) and dipropyl ketone (195) to the alkenes (196) and (197), respectively (Scheme 79). In this method, experiments have demonstrated that the hydrogen is derived from the water, as indicated in Scheme 79, and thatTMEDA is an excellent solvent. The vinyllithium intermediate (190) may be trapped by other electrophiles thus, with carbon dioxide and DMF, the reaction affords ,[i-unsaturated carboxylic acids and aldehydes like (198) and (199) (Scheme 80). 

Introduction.—The oxidative dehydrogenation of alcohols to aldehydes and ketones over various catalysts, including copper and particularly silver, is a well-established industrial process. The conversion of methanol to formaldehyde over silver catalysts is the most common process, with reaction at 750—900 K under conditions of excess methanol and at high oxygen conversion selectivities are in the region 80—95%. Isopropanol and isobutanol are also oxidized commercially in a similar manner. By-products from these reactions include carbon dioxide, carbon monoxide, hydrogen, carboxylic acids, alkenes, and alkanes. 

Reaction of l-chloro-4,4-bis(chloromethyl)pentane with magnesium in diethyl ether, followed by quenching with carbon dioxide, gave 4-(l-methylcyclopropyl)butanoic acid in 68% yield. Cyclopropane derivatives with electron-withdrawing substituents 5 were prepared by elec-troreductive dechlorination of 2,4-dichlorobutanoic acid derivatives in dimethyl sulfoxide solution in the presence of tetraethylammonium 4-toluenesulfonate at ambient temperature (yields 51 -90%).The starting materials for compounds 5 can easily be obtained by copper (I)-catalyzed photochemical addition of dichloromethane to electron-deficient alkenes. Electrochemical reductive 1,3-debromination has also been achieved however, it is of little synthetic value (experimental details are described in ref 16, with yields ranging from 39 to 94%). meso- and dimethyl sulfoxide gave equal amounts of cis- and transA, 2-dimethylpropane. ... 

Another way to deactivate carbanion is by reaction of the carbanion with carbon dioxide and dilute acid to give carboxylic terminal group or by reaction with alkene oxide (epoxide) to give a terminal alcohol. 

However, till now catalytic reactions of ethene and carbon dioxide are not known. But the great number of successful stoichiometric reactions between these two molecules makes it probable to achieve the catalytical bond formation in the near future. A short survey about the various reactions of ethene and other alkenes with carbon dioxide is given in the following sections in the order of transition metals applied. 

The reactions of carbon dioxide with alkenes (Chapter 1) and dienes (Chapter 2) presumably proceed via different mechanistic pathways. 

More interestingly, Ru3(CO)i2 dissolved in 1,3-dialkylimidazolium-based ionic liquids, in particular those associated with chloride anion [49], effectively catalyzed the hydroformylation of various kinds of alkenes with carbon dioxide to give the corresponding alcohols (Table 6.2). Compared to the conventional reaction, this reaction proceeded in the biphasic system, where the chemoselectivity in the... 

Oxalic and malonic acids, as well as a-hydroxy acids, easily react with cerium(IV) salts (Sheldon and Kochi, 1968). Simple alkanoic acids are much more resistant to attack by cerium(IV) salts. However, silver(I) salts catalyze the thermal decarboxylation of alkanoic acids by ammonium hexanitratocerate(IV) (Nagori et al., 1981). Cerium(IV) carboxylates can be decomposed by either a thermal or a photochemical reaction (Sheldon and Kochi, 1968). Alkyl radicals are released by the decarboxylation reaction, which yields alkanes, alkenes, esters and carbon dioxide. The oxidation of substituted benzilic acids by cerium(IV) salts affords the corresponding benzilic acids in quantitative yield (scheme 19) (Hanna and Sarac, 1977). Trahanovsky and coworkers reported that phenylacetic acid is decarboxylated by reaction with ammonium hexanitratocerate(IV) in aqueous acetonitrile containing nitric acid (Trahanovsky et al., 1974). The reaction products are benzyl alcohol, benzaldehyde, benzyl nitrate and carbon dioxide. The reaction is also applicable to substituted phenylacetic acids. The decarboxylation is a one-electron process and radicals are formed as intermediates. The rate-determining step is the decomposition of the phenylacetic acid/cerium(IV) complex into a benzyl radical and carbon dioxide. 

There is no clear reason to prefer either of these mechanisms, since stereochemical and kinetic data are lacking. Solvent effects also give no suggestion about the problem. It is possible that the carbon-carbon bond is weakened by an increasing number of phenyl substituents, resulting in more carbon-carbon bond cleavage products, as is indeed found experimentally. All these reductive reactions of thiirane dioxides with metal hydrides are accompanied by the formation of the corresponding alkenes via the usual elimination of sulfur dioxide. 

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