Carboxylic acids to imides

Amination of Free Carboxylic Acids to Amides and Imides... 

Telechelic dienes for metathesis polycondensation, containing functional groups such as those in alcohols, esters, carboxylic acids and imides, can be obtained via acyclic diene metathesis depolymerisation [64,65]. They can then be used in further reactions to create hydrophobic polyurethanes and other special-purpose polymers [1]. 

Food, flavors consist of numerous compounds, none of which alone is characteristic of specific food. Classes of compounds which emcompass food flavors are - hydrocarbons (aliphatic, ali-cyclic, aromatic) carbonyls (aldehydes, ketones) carboxylic acids, esters, imides, anhydrides alcohols, phenols, ethers alkylamines, alkylimines aliphatic sulfur compounds (thiols, mono-, di- and tri-sulfides) nitrogen heterocyclics (pyrroles, pyrazines, pyridines) sulfur heterocylics (thiophenes, thiazoles, trithiolane, thialidine) and oxygen-heterocyclics (lactone, pyrone, furan). Discussion will be limited to striking developments in heterocyclics. 

Selenenamides (23) are obtained by the substitution of selenenyl halides with amines or by the metathesis of the former compounds with Af-silylamines. N-(Phenylseleno)phthalimide (24) is similarly obtained using potassium phthalimide (Scheme 10). These compounds can be isolated but are prone to hydrolyze when exposed to moisture. Selenenamides react with aldehydes or jS-dicarbonyl compounds to afford a-seleno derivatives (as in the process shown in equation 11), and add to activated double and triple bonds, as in the example in equation (19). The imide (24) is a useful alternative to PhSeCl in various selenenylation reactions, and to ArSeCN in the conversion of alcohols and carboxylic acids to selenides and selenoesters (8), as shown in Scheme 3. 

Phenylsclenenyl triflate shows highly electrophilic character since it reacts even at — 78 °C with unsaturated carboxylic acids to afford the corresponding lactones. In some cases, the reaction of selenyl halides in the presence of the nucleophilie halide anion causes unfavorable side reactions, such as addition of the halogen atom, and decreased stereoselectivity. On the other hand, reactions of Ar-(phenylseleno)imides, which are not effected by the nucleophile, require a strong acid catalyst because of their lower reactivity. 

Reactions. The recent reacts with a carboxylic acid to form an imide. Succinic acid and phthalic acid are converted by the reagent into the anhydrides, but the... 

For instance, the reaction of amines with carboxylic acids occurs under appreciably milder conditions if phosphorus trichloride is added the reaction does not proceed by way of the intermediate acid chloride, as previously assumed, but the amine and phosphorus trichloride first form a phosphorazo compound (phosphoramidic imide) which in turn reacts with the carboxylic acid to give the amide 693... 

Isocyanates can react with both anhydrides and carboxylic acids to produce high molecular weight polymers. Poly(amide imide)s prepared by this route have actually achieved technical importance as high temperature varnishes and fibers [193,194]. Another approach is to make diisocyanates to react with imide-containing diacids as illustrated in Scheme (38). 

Microwave radiation can be used in the synthesis of alkyl azides. The microwave-assisted synthesis of j8- and 7-azidoarylketones 89 from haloaryUcetones 88 and NaNs leads to acceleration in reaction rates and yields comparable to the ones using conventional heating. The microwave-enhanced nucleophilic substitution approach to alkyl azides (91, 93 and 95) in aqueous medium from halides or tosylates and NaN3 is also known. The authors observed that a variety of reactive functional groups are tolerated, namely ester, carboxylic acid and imide (Scheme 3.12). 

AijAT-dicyclohexylcarhodiimide (DCC) also leads to essentially quantitative conversion of amic acids to isoimides, rather than imides (30,31). Combinations of trifluoroacetic anhydride—triethjlarnine and ethyl chi oroform a te—triethyl amine also result in high yields of isoimides (30). A kinetic study on model compounds has revealed that isoimides and imides are formed via a mixed anhydride intermediate (12) that is formed by the acylation of the carboxylic group of amic acid (8). 

For less hindered carboxylic acids acylation of the imidate requires only 5 minutes. With this modification the /V-(a-methoxybenzyl)amides are prepared according to the above-mentioned procedure [R = CH3, CH(CH,)2. CH(CH, )OAc, CH(C H2)OAc yield 85-88%]. 

The condensation reactions described above are unique in yet another sense. The conversion of an amine, a basic residue, to a neutral imide occurs with the simultaneous creation of a carboxylic acid nearby. In one synthetic event, an amine acts as the template and is converted into a structure that is the complement of an amine in size, shape and functionality. In this manner the triacid 15 shows high selectivity toward the parent triamine in binding experiments. Complementarity in binding is self-evident. Cyclodextrins for example, provide a hydrophobic inner surface complementary to structures such as benzenes, adamantanes and ferrocenes having appropriate shapes and sizes 12) (cf. 1). Complementary functionality has been harder to arrange in macrocycles the lone pairs of the oxygens of crown ethers and the 7t-surfaces of the cyclo-phanes are relatively inert13). Catalytically useful functionality such as carboxylic acids and their derivatives are available for the first time within these new molecular clefts. 

Carboxylic acids may be covalently modified with adipic acid dihydrazide or carbohydrazide to yield stable imide bonds with extending terminal hydrazide groups. Hydrazide functionalities don t spontaneously react with carboxylate groups the way they do with aldehyde groups (Section 4.5, this chapter). In this case, the carboxylic acid first must be activated with another compound that makes it reactive toward nucleophiles. In organic solutions, this may be accomplished by using a water-insoluble carbodiimide (Chapter 3, Section 1.4) or by creating an intermediate active ester, such as an NHS ester (Chapter 2, Section 1.4). 

Most proteins contain an abundance of carboxylic acid groups from C-terminal functionalities and aspartic and glutamic acid side chains. These groups are readily modified with bis-hydrazide compounds to yield useful hydrazide-activated derivatives. Both carbohydrazide and adipic acid dihydrazide have been employed in forming these modifications using the carbodi-imide reaction (Wilchek and Bayer, 1987). 

The thioimides can be hydrolyzed to the corresponding di-carboxylic acids. The thioimides can be converted to the corresponding imides, and thiohomophthalimides can be converted to phthalimides both conversions are one-step processes.4 Thus a variety of substituted phthalic and homophthalic acids and their derivatives are available from these thioimides. 

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