Unsaturated compounds carboxylic adds

However, the alcohol and acid formed during the hydrolysis of nitric esters are accompanied by a range of other compounds such as aldehydes, ketones, hydroxy-carboxylic acids, unsaturated hydrocarbons, nitrous add, etc. (e.g. reference [107]). 

Thiocarboxylic acids add to unsaturated compounds, affording 5-alkyl thiocarboxylates, which can be hydrolysed to mercapto carboxylic acids.43 Thioacetic acid always adds in such a way that the acetylthio group becomes attached to the carbon atom in jS-position to the carboxylate group ... 

So far we have shown you conjugate additions mainly of a,P-unsaturated aldehydes and unsaturated a,P-ketones. You won t be at all surprised to learn, however, that unsaturated acids, esters, amides, and nitriles—in fact all carboxylic acid derivatives—can also take part in conjugate addition reactions. Two examples, an amide and an ester, are shown on the right below. But notice how the selectivity of these reactions depends on the structure of the unsaturated compound compare the way butyllithium adds to this a,P-unsaturated aldehyde and a,P-unsaturated amide. Both additions are irreversible, and BuLi attacks the reactive carbonyl group of the aldehyde, but prefers conjugate addition to the less reactive amide. Similarly, ammonia reacts with this acyl chloride to give an amide product that derives from direct... 

The Knoevenagel reaction in its simplest form is the condensation of malonic esters (or their analogues) with aldehydes or ketones in the presence of an amine base catalyst plus a small amount of a carboxylic add (or amino add) cocatalyst. The condensation products are often a,p-unsaturated carbonyl compounds. For example. 

Can we use any of the acyl anion equivalents that we met in Section 20.2.2 to make 1,4-difunc-tionalized compounds This should work if, instead of adding them directly to a carbonyl compound, we add them to an a,p-unsaturated species. Thus, we can add cyanide to an enone (Figure 20.30), and the product can be hydrolyzed to a carboxylic acid, reduced to an amine, or otherwise elaborated. Remember that simple nucleophiles such as cyanide undergo conjugate addition to enones under conditions of thermodynamic control. 

The benzotriazolyl derivative of acrolein acetal, compound 882, is lithiated, treated with chlorodiphenylphosphine, and the obtained intermediate is oxidized with hydrogen peroxide to phosphine oxide 883 (Scheme 145). The relatively acidic proton in derivative 883 is easily removed by a base, and the obtained anion adds to a carbonyl group of aldehyde or ketone. Subsequent rearrangement and elimination of the phosphorane group generates diene 884. For the derivatives of aldehydes (884, R2 = H), (E)-(E) stereoselectivity of the elimination is observed. Acidic alcoholysis of dienes 884 affords esters of P,y-unsaturated carboxylic acids 885 < 1997JOC4131>. 

Unsaturated polyesters are prepared through a classical esterification process. Typically, a dihydroxy compound, or mixtures of dihydroxy compounds, are treated with maleic anhydride and/or together with other dicarboxylic acids such as aromatic or aliphatic dicarboxylic acids under elevated temperature to remove the water produced during esterification process. Although various catalysts will catalyze this esterification reaction, there is enough carboxylic acid in the mixture so that it is not necessary to add extra catalyst. 

The aluminum tellurolate is very sensitive towards air and moisture and, therefore, is not isolated but used in situ. Aluminum benzenetellurolates add to a-enones and to oc,fi-unsaturated carboxylic acid esters. The adducts can be hydrolyzed to /i-phenyltelluro carbonyl compounds or reacted with an aldehyde1. 

Diisobutylaluminum benzenetellurolate, prepared from diphenyl ditellurium and diisobutylaluminum hydride, adds in a 1,4-fashion to a,/i-unsaturated aldehydes, ketones, and carboxylic acid esters to give as intermediates /i-phenyltelluro-substituted aluminum enolates that can be hydrolyzed to the carbonyl compounds or reacted with aldehydes to produce aldol adducts2. 

Af-Unsubstituted pyrazoles and indazoles add to compounds containing activated double and triple bonds (67HC 22)1,B-76MI40402>. Amongst C—C double and triple bonds, maleic anhydride, acrylic acid esters and nitriles, acetylene-carboxylic and -dicarboxylic esters (78AHC(23)263), quinones, and some a,/3-unsaturated ketones have been used with success. Phenylacetylene reacts with pyrazole in the presence of Na/HMPT as catalyst to yield the Z isomer of 1-styrylpyrazole in a highly stereoselective reaction (78JHC1543). 

Carbonyl compounds rapidly equilibrate with their ends, a process called tautomerism. Although end tautomers are normally present to only a small extent at equilibrium and can t usually be isolated in pure form, they nevertheless contain a highly nucleophilic double bond and react rapidly with electrophiles. For example, ketones and aldehydes are rapidly halogenated at the a position by reaction with C . Br2, or I2 in acetic acid solution. Alpha bromination of carboxylic acids can be similarly accomplished by the Hell-Volhard-Zelinskii (HVZ) reaction, in which an add is treated wdth Br2 and PBr. The u-halogenated products can then undergo base-induced E2 elimination to yield a, -unsaturated carbonyl compounds. 

Heterosubstituted cydopropanes can be synthesized from appropriate olefins and car-benes. Since cydopropane resembles olefins in its reactivity and is thus an electron-rich carbo-cycle (p. 76ff.), it forms complexes with Lewis adds, e.g. TiCU, and is thereby destabilized. This effect is even more pronounced in cyclopropanone ketals. If one of the alcohols forming the ketal is a silanol, the ketal is stable and distillable. The O—Si-bond is cleaved by TiCl4 and a d3-reagent is formed. This reacts with a1-reagents, e.g. aldehydes or ketals. Various 4-substituted carboxylic esters are available from 1-alkoxy-l-siloxycyclopropanes in this way (E. Nakamura, 1977). If one starts with l-bromo-2-methoxycyclopropanes, the bromine can be selectively substituted by lithium. Subsequent treatment of this reagent with carbonyl compounds yields (2-methoxycyclopropyl)methanols, which can be transformed to / ,y-unsaturated aldehydes (E.J. Corey, 1975B). 

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