Alkenes, with acids metal salts

In a similar vein, a series of papers published between 2002 and 2008 contains spectacular claims of highly enantioselective asymmetric additions of water to styrenes, unsaturated carboxylic acids, or simple terminal alkenes [34-Al]. The catalysts used are of the heterogeneous type and based on chiral biopolymers such as wool, gelatin, or chitosan as solid supports (sometimes in combination with silica or ion-exchange resins) that are doped with transition metal salts. This series of papers contains spectacular claims, insufficient experimental data, and erroneous chemical structures for the biopolymers used. As earlier work from the same group of authors on asymmetric catalysis on bio-polymeric supports is irreproducible [42], one is well advised to await independent confirmation of those results. 

It is not out of place to give brief mention to the ionomers introduced by Du Pont in the mid-1960s. To produce these polymers an alkene, usually ethylene, is copolymerized with a few per cent of a second monomer such as an -carboxylic acid in order to introduce a few carboxylic acid groups into the chain. The copolymer is then blended with a metal salt which ionizes the acid group. Heat fugitive ionic cross-links form (between carboxylic groups via the metal... 

In 1965, Denney et al. (98) reported the reaction of a number of alkenes with ferf-butyl hydroperoxide (TBHP) and cupric salts of chiral acids. The use of ethyl camphorate copper complex 144 in the allylic oxidation of cyclopentene provides, upon reduction of the camphorate ester, the allylic alcohol in low yield and low selectivity, Eq. 82. The initial publication only provided the observed rotation of cyclopentenol, but comparison to subsequent literature values (99) reveals that this reaction proceeds in 12% ee and 43% yield (based on the metal complex). 

Anodic oxidation of 1,2-dicarboxylic acids as their alkali metal salts in concentrated aqueous solution gives the alkene with the loss of two molecules of carbon dioxide [125]. Succinic acid affords etltene and methylsuccinic acid ptopene [50]. Allene is obtained from itaconic acid and the isomeric methylmaleic and methyl-fumaric acids give propyne... 

Hydroamination of Alkenes Kobayashi et at. found that several transition metal salts displayed high catalytic activity in aza-Michael reactions of enones with carbamates, while conventional Lewis acids (BF3-OEt2, A1C13, TiCl4...) were much less active. 

According to Eq. (17), AGd° is negative if AG 0 < AG. A value of -50 kJ mol-1 was estimated for AGa° (-70° C) above, so that carbocation salts can only add to olefins to form covalent products if AG > -50 kJ mol-1. As AG depends both on the structure of R+ and on the Lewis acidity of MCI, we can conclude that the thermodynamic driving force for Case d increases with decreasing stabilization of R+ and decreasing chloride-ion affinity of MC1 . Because the magnitude of AG can be estimated from the relative chloride affinities of carbocations and Lewis acidic metal halides in Scheme 7 (Section II.G), one can derive which carbocationic salts might add to alkenes with formation of covalent products. 

The pyrolytic decomposition of the sodium salts of various fluorinated carboxylic acids to give isomeric unsaturated compounds has also been reported. The products were identified as alkenes with the C = C bond inside the carbon chain, mainly alk-2-enes. This isomerization may be catalyzed by the coal-like products formed during the pyrolytic decarboxylation of the salts, but the metal fluoride formed in the reaction may also be responsible for the isomerization. When potassium perfluoro(5-chloropentanoate) is heated in a rocking autoclave at 300 C for 2 hours, perfluorobut-2-ene (2b) is isolated in 82% yield.This is only possible by migration of the double bond away from the terminal position after carbon dioxide elimination and halogen exchange to form potassium chloride. ... 

It was noted that for the perfluorobutanoic acid salts of the alkaline earth metals the yield of perfluoroalkene increased with increasing weight of the metal cation (vide supra). Decomposition of the barium salt gave hexafluoropropene in 78% yield while the reaction with the magnesium salt gave > 5 % of the same product. An exception was ammonium per-fluorobutanoate (4) which formed no alkene, but instead gave an almost quantitative yield of... 

A number of metals salts can be used as the source of electrophiles in reactions with alkenes. One of the most interesting of these involves the attack of mercury(II) acetate in acetic acid. Reductive cleavage of the organomercury compound with sodium borohydride leads to the overall hydration of the alkene in a Markownikoff sense. There are a number of preparative advantages, such as a reduced tendency to rearrange, associated with this and similar relatively mild procedures when compared to the direct protonation of a double bond (Scheme 3.14)... 

The acid-catalyzed hydrocarboxylation of alkenes (the Koch reaction) can be performed in a number of ways. In one method, the alkene is treated with carbon monoxide and water at 100-350°C and 500-1000-atm pressure with a mineral acid catalyst. However, the reaction can also be performed under milder conditions. If the alkene is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0-50°C and 1-100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 10-77). Nearly all alkenes can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. Hydrocarboxylation can also be accomplished under mild conditions (160°C and 50 atm) by the use of nickel carbonyl as catalyst. Acid catalysts are used along with the nickel carbonyl, but basic catalysts can also be employed. Other metallic salts and complexes can be used, sometimes with variations in the reaction procedure, including palladium, platinum, and rhodium catalysts. The Ni(CO)4-catalyzed oxidative carbonylation with CO and water as a nucleophile is often called Reppe carbonylationP The toxic nature of nickel... 

Alkenes are converted to epoxides by oxidation with peroxy acids, and thereby they are protected with regard to certain chemical transformations. Alkaline hydrogen peroxide selectively attacks enone double bonds in the presence of other alkenes. The epoxides can be transformed back to alkenes by reduction-dehydration sequences or using triphenylphosphine, chromous salts, zinc, or sodium iodide and acetic acid. A more advantageous and fairly general method consists, however, of the treatment of epoxides with dimethyl diazomalonate in the presence of catalytic amounts of binuclear rhodium(II) car-boxylate salts. This deoxygenation proceeds under neutral conditions and without isomerization or cy-clopropanation of the liberated alkene (Scheme 97). Furthermore, epoxides can be converted to alkenes with the aid of various metal carbonyl complexes. Thus, they may be nucleophilically opened with... 

Arylcyclopropanes are also obtained in good yields by decomposition of aryldiazomethanes with various metals and salts in the presence of an alkene. The reactions do not involve free carbenes, but carbene-metal complexes, and this is probably the reason why the cisjtrans ratios for the arylcyclopropanes vary when the catalyst is changed. Thus, when 4-tolylcarbene, generated by decomposition of 4-tolyldiazomethane with various salts, was allowed to react with (Z)-but-2-ene the cisjtrans ratio of the product, cw-2,3-dimethyl-l-(4-tolyl)cyclopropane (1), varied considerably. When the decomposition is facilitated by trifluoroacetic acid, however, 1 is obtained with a cisjtrans ratio of 1 1. ... 

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