Acylation of amides

Amination of anhydrides 0-58 N-Alkylation of imides 0-59 N-Acylation of amides or imides 5-7 Addition of imides to olefins... 

The intermolecular N-acylation of amides generally requires treatment of the latter with strong acylating agents, such as ketenes, acyl halides, or anhydrides, in the presence of a base. Few examples of such N-acylations have been reported (Entries 1-3, Table 13.20 see also saftey-catch linkers, Section 3.1.2.3). 

A similar reaction can be used for acylation of amides with acid chlorides. Example ... 

Acylation of amide bonds in peptides can be accomplished by silylation with trimethylsilyl chloride followed by treatment with acid chlorides. A modified procedure has been applied to acylation of the sensitive 3-lactam antibiotic cephamycin, where silylamides like trimethylsilylurethane trap generated HCl (equation 54). ... 

Bismuthinate-mediated A -acylation of amides with carboxylic acids... 

Bismuthinate-mediated A -acylation of amides with carboxylic acids 321 Chlorination of alcohols with trimethylsilyl chloride in the presence of a catalytic amount of BiCla 430... 

Acylation of amides is naturally much harder to achieve, because of their lower basicity, but it is very greatly facilitated by the presence of pyridine.583 617 618 The reason for this effect is, of course, the intermediate formation of 1-acylpyridinium salts as mentioned above.619 For instance, dibenzamide is formed almost quantitatively from benzoyl chloride and benzamide in pyridine solution even at room temperature, whereas there is no reaction in the absence of pyridine.620 Also, by the action of aromatic acid halides on aliphatic or aromatic amides in the presence of pyridine at temperatures as low as —60° to —70° Thompson617 obtained high yields of triacyl derivatives. 

Other methods for the acylation of amides without the use of pyridine generally call for considerably more energetic conditions than are required for amines. For instance, many hours boiling under reflux are necessary for mono- or di-acylation of urea by fatty acid halides.621 622... 

Aldehydes react with the lithio-derivatives of a-diazo-esters to give /3-hydr-oxy>a-diazo-esters, which in turn undergo rhodium(ii)-catalysed decomposition to give /3-keto-esters./3-Keto-amides are obtained in moderate to high yield from the acylation of amide enolates with mixed anhydrides. In a general reaction, orthoformates react with acidic methines to give /3-keto-aldehydes, isolated as their dialkyl acetals [equation (16)]. ... 

Figure 6.34 Use of bromo[ C]acetyl bromide in N-acylation of amides, imides and sulfonamides preparation of (2S-N-bromo[ " C]acetyl)bornane-10,2-sultam...

Amides are readily prepared by acylation of ammonia and amines with acyl chlorides acid anhydrides or esters... 

Acyl derivatives, RCO—NH—OH and HjN—O—CO—R, are named as A-hydroxy derivatives of amides and as O-acylhydroxylamines, respectively. The former may also be named as hydroxamic acids. Examples are A-hydroxyacetamide for CH3CO—NH—OH and O-acetylhydrox-ylamine for HjN—O—CO—CH3. Further substituents are denoted by prefixes with O- and/or A-locants. For example, C5H5NH—O—C2H5 would be O-ethyl-A-phenylhydroxylamine or A-ethox-ylaniline. 

Ketone formation can also be avoided if one of the functional acyl halogens ia phosgene is blocked. Carbamyl chlorides, readily obtained by the reaction of phosgene with ammonia or amines, are suitable reagents for the preparation of amides ia direct Friedel-Crafts acylation of aromatics. The resulting amides can be hydroly2ed to the corresponding acids (134) ... 

MPD-1 fibers may be obtained by the polymeriza tion of isophthaloyl chloride and y -phenylenediamine in dimethyl acetamide with 5% lithium chloride. The reactants must be very carefully dried since the presence of water would upset the stoichiometry and lead to low molecular weight products. Temperatures in the range of 0 to —40° C are desirable to avoid such side reactions as transamidation by the amide solvent and acylation of y -phenylenediamine by the amide solvent. Both reactions would lead to an imbalance in the stoichiometry and result in forming low molecular weight polymer. Fibers are dry spun direcdy from solution. 

The reverse reaction is an intramolecular acidolysis of amide group by the o-carboxyhc acid to reform anhydride and amine. This unique feature is the result of an ortho neighboring effect. In contrast, the acylation of an amine with ben2oic anhydride is an irreversible reaction under the same reaction conditions. The poly(amic acid) stmcture (8) can be considered as a class of polyamides. Aromatic polyamides that lack ortho carboxylic groups are very... 

Carboxylic Acid Group. Reactions of the carboxyl group include decarboxylation, reduction to alcohols, and the formation of salts, acyl hahdes, amides, and esters. 

The formation of amides can be accompHshed by dehydration of the ammonium salts of sahcyhc acid. The more common method for amines is the reaction of the ester, acyl hahde, or anhydride with an amine or ammonia. Each step is fast and essentially irreversible. 

Several triazinyl ketones isomerize to 4-acetamidopyrimidines. TTiis is seen in the C-acylation of 2,4,6-trimethyl-l,3,5-triazine (708) with benzoyl chloride in the presence of sodium amide to give the ketone (709) which undergoes a Dimroth-like rearrangement in boiling water to afford A-(2-methyl-6-phenylpyrimidin-4-yl)acetamide (710) it can be seen that the acylating agent determines the identity of the 6-substituent 64JHC145). 

The second reaction that should be recalled is the aminolysis of esters (p. 479). This reaction leads to the formation of amides by N-acylation ... 

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