Unsaturated acids, transfer

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

When studying the free-radical copolymerization of methacrylic and acrylic acids with vinyl monomers, it was established that the addition of catalytic amounts of SnCl and (C6Hs)3SnH has a marked effect on the copolymer composition. It was found that complexes are formed by charge transfer between unsaturated acids and the above tin compounds. It has been suggested that the change in polymer composition is caused by the interaction of the tin compounds with a transition complex resulting in a decrease of the resonance stabilization of the latter 94,). 

A typical atom transfer sensitization process is shown in Figure 3.7 the alkylation of an unsaturated acid via a radical produced from an alcohol by hydrogen abstraction (in a green solvent, water). This principle has been applied to a large series of radical alkylation reactions, where the radical precursor is an alcohol, an ether, or even an alkane. ... 

Allyl chlorides and bromides are readily carbonylated to unsaturated acids using nickel cyanide and phase transfer catalysis conditions. Mechanistic studies revealed that the key catalytic species in this reaction is the cyanotricarbonylnickelate ion(20). 

Phase-transfer catalysis has been developed by the combination of Keggin-type heteropolyanions and quaternary countercations such as tetrahexyl-ammonium or cetylpyridinium ion. The oxidations of alcohols (306), allyl alcohols (307), olefins (308), alkynes (309), /J-unsaturated acids (310), v/ c-diols (311), phenol (312), and amines (313) are the examples. 

Reduction of conjugated diunsaturated acids.3 a,/ y, 5-Diunsaturated acids are reduced by sodium dithionite in an alkaline medium (NaOH, NaHC03) to a mixture of (Z)- and (E)-/J,y-unsaturated acids (40 75% yield). A similar reduction of the diunsaturated esters is possible under phase-transfer conditions (Adogen 464, C6H6-HzO). 

The ionization constants of a series of hindered polynuclear aromatic acids have been determined by Newman and Boden (1961). Two factors are held to affect the acidic strength of such acids the decrease of solvation and the inhibition of resonance due to steric effects. Solvation of an ion should be an acid-strengthening factor and if steric factors decrease the amount of anion solvation, the acid should be correspondingly weaker. The resonance factor only comes into play with aromatic (or unsaturated) acids. Here resonance would involve transfer of... 

Unfortunately, several important classes of a-diazo ketones cannot be prepared in good yield via these standard methods. a -Diazo derivatives of a.p-unsaturated ketones, for example, have previously proved to be particularly difficult to prepare.1113 12 The acylation of diazomethane with a.p-unsaturated acid chlorides and anhydrides is generally not a successful reaction because of the facility of dipolar cycloaddition to conjugated double bonds, which leads in this case to the formation of mixtures of isomeric pyrazolines. Also problematic are diazo transfer reactions involving base-sensitive substrates such as certain a,p-enones and heteroaryl ketones. Finally, the relatively harsh conditions and lack of regioselectivity associated with the thermodynamically controlled Claisen formylation step in the "deformylative" diazo transfer procedure limit the utility of this method when applied to the synthesis of diazo derivatives of many enones and unsymmetrical saturated ketones. 

Evaporate the solvent from the filtrate on the steam bath and evacuate the residual fraction of unsaturated acids at the aspirator until the weight is constant. The yield of a mixture of stearic and palmitic acids is 5-7 g. In a second 125-mL Erlenmeyer flask dissolve 11 g of urea in 50 mL of methanol and pour the solution onto the unsaturated acid fraction. Reheat to dissolve any material that separates and let the solution stand until a large crop of needles has separated. Then cool thoroughly in an ice bath with swirling, collect the product, and rinse the flask with filtrate. Press down the crystals and drain to promote rapid drying and spread out the needles on a large filter paper. After a few minutes, transfer the crystals to a fresh paper. The yield of colorless oleic acid-urea inclusion complex is 10-12 g. The complex does not have a characteristic melting point. 

Electrochemical reduction of coumarin [187] affords the meso and ( ) forms of a product hydrodimerized (at C-4) like many other a,)6-unsaturated acid derivatives. In the presence of tertiary amines, which are not destroyed during the process but catalyze the evolution of hydrogen, a transfer of hydrogen takes place from the amine radical to the coumarin radical with formation of 3,4-dihydrocoumarin. Asymmetric amines cause asymmetric induction during the reduction of 4-methylcoumarin, as in Chapter 26 [188]. 

By derivatizing an a,p-unsaturated acid into the mono ester of chiral 1,1 -bi-8,8 -naphthol the reaction with lithium dialkylcuprates leads to saturated ketones containing chirality centers at the p-carbon atoms." Consecutive 1,4-addition and 1,2-addition account for this result. The alkyl transfer to enones from Grignard reagents under copper catalysis is subject to chiral modification, e.g., by the introduction of 56" or 57." ... 

A plausible mechanism for the reaction includes several organometallic species that are sensitive to reactive moieties elsewhere in the molecule. If a chloro, chloromethyl, or mesyloxymethyl substituent is attached vicinal to the 1,1 -dibromo moiety, efficient ring opening occurs prior to carbonylation and P,y- and y, -unsaturated acid derivatives are formed. Reductive carbonylation has also been achieved with 1,1-dibromocyclopropanes using an excess of pentacarbonyliron in dimethylformamide with added methanol or sodium methoxide, or cobalt(II) chloride and nickel(ll) cyanide under phase-transfer conditions in a carbon monoxide atmosphere. However, the yield of cyclopropanecarboxylic acid derivatives is low, and when pentacarbonyliron is used the amount of monobromides is fairly high. ... 

In contrast to the mechanism of equation (d), which is based on hydride transfer from [CoH(CN)j] , detailed kinetic studies with some a,)8-unsaturated acids, esters, and nitriles indicate successive hydrogen atom transfers to uncoordinated substrates from [Co"(CN)5( H)] species equations (e), (f) . 

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