Acyl imidates carboxylic acid amides

Acyl imidates from carboxylic acid amides C(0)NH C(OAc) = N... 

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%]. 

Imides can be prepared by the attack of amides or their salts on acyl halides, anhydrides, and carboxylic acids or esters. The best synthetic method for the preparation of acyclic imides is the reaction between an amide and an anhydride at 100°C catalyzed by H2S04. When acyl chlorides are treated with amides in a2 l molar ratio at low temperatures in the presence of pyridine, the products are N,N-diacylamides, (RCO)3N. ... 

This chapter is concerned with the cathodic reduction of carboxylic acids and their derivatives, that is, esters, amides, anhydrides, acyl halides, hydrazides, nitriles, and corresponding thio derivatives. Cyclic derivatives of substituted carboxylic and polycarboxylic acids, such as lactones, lactams, imides, and anhydrides, are also included. Only those transformations in which the functional group itself is involved are discussed. Reductive coupling of carboxylic acids and derivatives is covered in Chapter 22, and there is some overlap with reduction of heterocycles in Chapter 18. 

Alkylations of acyclic enolates containing a collection of chiral auxiliary groups have been used successfully for the asymmetric synthesis of carboxylic acids. The chiral, nonracemic substrates that have been used include amides, imides, esters, imine derivatives of glycinates and acyl derivatives of chiral transition metals. In these systems either extraannular or chelate-enforced intraannular chirality transfer may control the sense of the alkylation step. 

Aside from the outstanding and reliable diastereoselectivity, two more advantageous features helped the method to success the easy, one-step preparation of various N-acylated derivatives from the parent oxazolidinones and the cleavage of the auxiliary by hydrolysis, transamidation to the Weinreb amide, esterification, and reduction, as outlined in Section 4.1. A typical Evans aldol procedure with phenylalanine-derived oxazolidinone (S)-47, including the preparation of propionic imide 73 and cleavage of the auxiliary, is shown in Scheme 4.47. Typically, the boron aldolate resulting from the addition to the aldehyde has to be cleaved by an oxidative work-up. The hydrolysis of the aldol adduct 211 occurs without detectable epimerization that liberates diastereomerically and enantiomerically pure carboxylic acid 212 besides the auxiliary (S)-47 [110]. 

Mixed anhydrides prepared from carboxylic acids and alkyl chlorocarbonates are of paricular value for the preparation of amides of sensitive acids such as A -acylated amino acids. The reaction of cyclic dianhydrides with amines yields imides. If diamines are used with dianhydrides, polyimide resins are produced. 

The chemical transformations of the carboxyl group include formation of halo[ C]acetyl halides, amides, imides, alcohols, aldehydes and amines. Methods for the preparation of halo[ " C]acetyl halides from [ " C]acetic acid have already been mentioned. In addition, chloro[ " C]acetyl chloride has become available through treatment of chloro[ C]acetic acid with thionyl chloride or phthaloyl chloride, whereas for bromo[ " C]acetyl chloride, thionyl chloride or phosphorus pentachloride is recommended. Numerous applications of halol Clacetyl halides have been published, out of which the following C-, N- and 0-acylations may illustrate their versatility. 

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