Unsaturated acids, selective

Carboxylic acids are produced in water. Selection of solvents is crucial and the carbonylation of the enol triflate 480 can be carried out in aqueous DMF, and that of the aryl triflate 481 in aqueous DMSO using dppf as a ligand[328,334]. The carbonylation of the enol triflate 482 to form the a, 0. unsaturated acid 483 using dppf as a ligand in aqueous DMF has been applied in the total synthesis of multifunctionalized glycinueclepin[335]. 

Multiply unsaturated linolenic and linoleic acid residues make triglycerides more vulnerable to oxidative degradation than oleic acid which is relatively stable. It is therefore desirable to hydrogenate the most unsaturated residues selectively without production of large quantities of stearic (fully saturated) acid. The stepwise reduction of an unsaturated oil may be visualized as ... 

Many of these cobalt complexes will catalyze the reduction of organic compounds by borohydride, hydrazine, thiols, etc. Cobalt cyanide complexes will catalyze the reduction of a,j8-unsaturated acids by borohydride (105) DMG complexes the reduction of butadiene and isoprene by borohydride, but not by H2 (124) Co(II) salen, the reduction of CHCI3 and CH3CCI3 to the dichloro compounds by borohydride (116) and cyanocobalamin, the selective reduction of -CCI2- by borohydride to -CHCl- in compounds such as aldrin, isodrin, dieldrin, and endrin without... 

BINAP (40a) was first reported as a ligand in an enantioselective hydrogenation in 1980 [172], and provides good selectivity for the reductions of dehydroamino acid derivatives [173], enamides, allylic alcohols and amines, and a,p-unsaturated acids [4, 9, 11, 12, 174, 175]. The fame of the ligand system really came with the reduction of carbonyl groups with ruthenium as the metal [11, 176]. The Rh-BINAP systems is best known for the enantioselective isomerizations... 

On the other hand, the methoxyester results from MeOH attack on coordinated double bond, followed by methoxycarbonylation (Scheme 11). In both cases, the formation of 7r-allylpalladium complexes directs the regio-chemistry of the process. By optimizing the reaction conditions, it has been possible to obtain the unsaturated diester selectively. The latter compound is particularly important, since it can be easily transformed after hydrolysis and hydrogenation into adipic acid [52-54], Selective alkoxy-alkoxycarbonylation of 1,3-dienes has also been achieved [55]. 

The photoelectrochemical synthesis of amino acids from simple molecules has also been reported. Low efficiencies were observed in the conversion of mixtures of methane, ammonia and water to several amino acids on platinized TiOz Amino acids and peptides were reported when glucose replaced methane as the carbon source in a parallel experiment Higher quantum efficiencies (20-40%) were observed in the conversion of alpha-keto acids or alpha-hydroxy acids to the corresponding alpha-amino acids Moderate levels of enantiomeric selectivity (optical yields of about 50%) were reported when chiral starting materials were employed. Photoinduced Michael-like reactions were observed when alpha, beta unsaturated acids were used as substrates for the amino acid synthesis... 

Alkene acylation may be used in the synthesis of cyclic products by appropriately selecting the alkene and the acid derivative. When a,P-unsaturated acid halides react with cycloalkenes, the intermediate undergoes cyclization to yield octalones and indanones 112... 

Three types of C-F bonds are encountered in unsaturated acids and their functional derivatives, namely nonactivated aliphatic, activated aliphatic (allylic, benzylic, and a to carbonyl), and vinylic bonds. The ease and selectivity of the reduction of C-F bonds is strongly dependent on the chemical environment. 

Hydrogenation.1 Hydrogenation of water-soluble unsaturated acids is best carried out on the sodium salt in an aqueous solution with a catalytic amount of the catalyst and triethoxy silane as the source of hydrogen. If only 1 equiv. of triethoxy-silane is added, triple bonds are selectively reduced to (Z)-alkenes in 70-85% yield. 

Hoskins and Crout6 have carried out the selective esterification of retronecine (12) at C-9 in moderate yield with simple acids using NN -dicyclohexylcarbodi-imide. With a/3-unsaturated acids and bulky a-trisubstituted acids, the use of /VJV -carbonyldi-imidazole, with prior formation of the acyl-imidazole, gave reasonable yields of the C-9 monoesters of (12). The regiospecificity of this... 

Many of the chiral selenium electrophiles have also been employed in cyclization reactions. Various internal nucleophiles can be used and access to different heterocycles is possible. Not only oxygen nucleophiles can be used for the synthesis of heterocyclic compounds, but also nitrogen nucleophiles are widely employed and even carbon nucleophiles can be used for the synthesis of carbacycles with new stereogenic centers. Oxygen nucleophiles have been widely used and some selected examples of selenolactonizations of unsaturated acids 50 and 52 and seleno-etherifications of unsaturated alcohols 54 and 56 are shown in Scheme 10. 

Enamines of acyclic and cyclic ketones react with 2,2-dimethoxyethyl esters of a,/ -unsaturated acids in the presence of titanium tetrachloride under very mild conditions to give the Michael adduct with high -selectivity. A reactive l,3-dioxolan-2-ylium salt is formed which reacts with the enamine via a chair-like transition state168... 

Although alkene hydrogenation is one of the easiest organic reactions, the partial hydrogenation of vegetable oils presents some selectivity problems to get the desired properties. For example, while it is necessary to reduce the number of unsaturations in order to harden the oil and reduce the sensitivity to oxidation, unsaturated acids are fundamental in our diet and thus it is important to keep at least part of them. 

Iodolactonization of yfi-unsaturated amides. Halolactonization (I2 or NBS) of a-substituted "y,8-unsaturated amides in DME/H,0 at room temperature gives predominantly fra/w-2,4-disubstituted y-butyrolactones (equation I). This 1,3-stereoselectivity is in sharp contrast to the moderate 1,3-cw-selectivity observed with a-substituted y,8-unsaturated acids (8,257 9,248). Both diastereomers of a, 3-disubstituted y.S-unsaturated amides are converted into 2.4-rram-2,3,4-trisub tituted lactones (equation II). 

Several cases have been reported in which the reactivity of the C-C douhle hond towards nucleophilic attack is further enhanced by an external electrophile. An example of an exo-trig cyclization induced by mercuration is shown in the case of the unsaturated acid rac-1 which was converted to the cyclic acetals (otR,2S)-2 and (y.S.2S)-2 employing mercury(ii) acetate in methanol followed by subsequent demercuration40. In the latter step, sodium trithiocarbonate afforded the highest selectivity in terms of retention of configuration (cf. Section 4.7.1.1.1.1.2.). 

Simple a-substituted styrenes are reduced in the presence of RuCl2(DuPhos)(DMF) . The reactivity of the ruthenium catalyst is enhanced by the addition of potassium te/t-butoxide, which may facilitate generation of a ruthenium hydride. The products are obtained under low hydrogen pressures and selectivities obtained are up to 89% ee (eq 8). Neutral Rh-DuPhos complexes catalyze the hydrogenation of a,3-unsaturated acids such as tiglic acid (eq 9). The product is obtained in quantitative yield and good enantioselectivity. ... 

Most natural triacylglycerols do not have a random distribution of fatty acids on the glycerol backbone. In plant oils, unsaturated acids predominate at the sn-2 position, with more saturated acids at sn-l and sn-3. The distribution of fatty acids at the sn-l and sn-3 positions is often similar, although not identical. However, a random distribution between these two positions is often assumed as full stereospecific analysis is a time-consuming specialist procedure. In animal fats, the type of fatty acid predominating at the sn-2 position is more variable for example, palmitate may be selectively incorporated as well as unsaturated acids (Table 5). 

Glick J, Santoyo G, and Casey PJ. (1996). Arachidonate and related unsaturated fatty acids selectively inactivate the guanine nucleotide-binding regulatory protein, Gz. J. Biol. Chem. 271,2949-2854. 

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