Carboxamides carboxylic esters

This chapter covers not only nuclear and extranuclear quinoxahnecarboxylic acids (and anhydrides) but also the carboxylic esters, acyl halides, carboxamides, carbohydrazides, carbonitriles, carbaldehydes, and (ketonic) acyl derivatives of quinoxaline a few related speceis are also included. To avoid repetition, the interconversions of these quinoxaline derivatives are discussed only at the first opportunity thus the esterification of quinoxalinecarboxylic acids in covered as a reaction of carboxylic acids rather than as a preparative route to carboxylic esters, simply because the section on carboxylic acids precedes that on carboxylic esters. To minimize any confusion, appropriate cross-references have been inserted. 

Finally, l,4-benzodioxin-2-carboxylic esters or carboxamides react with nucleophilic amines to give access to 3-hydroxy-2,3-dihydro-l,4-benzodioxin-2-carboxamides and 3-aminomethylene-l,4-benzodioxin-2(777)-one 263 <2003T1227>. 

When an amino group is adjacent to a carboxamide group, annulation usually leads to a pyrrolo[2,3-r/ pyrimidin-4-one 164. Such is the case when 163 is allowed to react with aliphatic carboxylic esters (Equation 61) <1996H(42)691>. 

Bordwell, F. G. Zhang, S. Zhang, X.-M. Liu, W.-Z. Homolytic bond dissociation enthalpies of the acidic H-A bonds caused by proximate substituents in sets of methyl ketones, carboxylic esters, and carboxamides related to changes in ground state energies./. Am. 

Dirhodium(II) tetrakis(carboxamides), constructed with chiral 2-pyrroli-done-5-carboxylate esters so that the two nitrogen donor atoms on each rhodium are in a cis arrangement, represent a new class of chiral catalysts with broad applicability to enantioselective metal carbene transformations. Enantiomeric excesses greater than 90% have been achieved in intramolecular cyclopropanation reactions of allyl diazoacetates. In intermolecular cyclopropanation reactions with monosubsti-tuted olefins, the cis-disubstituted cyclopropane is formed with a higher enantiomeric excess than the trans isomer, and for cyclopropenation of 1-alkynes extraordinary selectivity has been achieved. Carbon-hydro-gen insertion reactions of diazoacetate esters that result in substituted y-butyrolactones occur in high yield and with enantiomeric excess as high as 90% with the use of these catalysts. Their design affords stabilization of the intermediate metal carbene and orientation of the carbene substituents for selectivity enhancement. 

Many of the iV-alkyl and iV-aryl derivatives of urazine have been synthesized and characterized, but the parent substance is not well known. In the past, urazine has been prepared by thermal deammonation of carbohydrazide-iV-carboxamide [eq. (I)],1 fusion of hydrazidicarbamide with hydrazinium hydrogen sulfate [eq. (2)],2 fusion of earbohy-drazide with urea [eq. (3)],3 action of sodium hypobromite on semicarbazide [eq. (4)],4 reaction of dichlorourea with concentrated ammonia [eq. (5)],5 and the reaction between 1,2 hydrazine carboxylic ester and hydrazine hydrate... 

Thermal or photochemical treatment of isoxazoies 851 has been found to result in a ring-contraction reaction to produce acyl 277-azirines 852, which sometimes rearrange to form other heterocycles like oxazoles 853. This ring-contraction reaction can also be promoted by iron(ii) catalysts. Thus, 5-alkoxy- and 5-aminoisoxazoles isomerize to 27/-azirine-2-carboxylic esters and 2/7-azirine-2-carboxamides, respectively, in nearly quantitative yield by reaction with catalytic FeCb (Scheme 212) <1997T10911>. 

This ring is formed by reaction between a carboxamide and a carboxylic ester under strongly basic conditions. 

B/C, whereby the molecule assumes a sigmoidal conformation that allows both head groups to interact in identical mode with the SI pockets (Fig. 2.13). The (4-amino-methyl)benzyl group inserts into the SI pockets to a 2.6 A distance from the Asp 189 carboxylate, and additional hydrogen bonds with residues of the protease surface are coordinating the carboxamide and ester groups, while the hydrophobic spacer acts as an optimal tether (Figs. 2.13 and 2.14). 

Carboxamides used to cyclize 3-aminopyridine-4-carboxylic esters are formamide463-470-472 and acetamide.470 Heating the components at 170°C yields the pyrido[3,4-c/]pyrimidin-4(3//)-ones 13. 

Pyrazinyl ketones have been prepared by treatment of pyrazinecarboxylic esters with an organo-metallic (alkyllithium or Grignard) reagent <84MI 603-01 >. Homolytic acylation of pyrazines and quinoxalines with a-keto acids is an important method for preparation of the acyl compounds (Section 6.03.5.6.1), but the procedure for monosubstitution needs care because the electron-withdrawing effect of the first-formed monoacyl compounds facilitates further substitution. An additional synthesis of pyrazinyl ketones is the lithiation of halogenopyrazines followed by treatment with carboxylic esters or carboxamides (Equation (8) and Scheme 24). Reaction of 2-chloropyrazine... 

Ketone 265a Carboxylic Ester 264b Carboxamide 266a... 

In 1975, Teruaki Mukaiyama published two papers. One described the synthesis of carboxylic esters,2 and the other, carboxamides, by using l-methyl-2-halopyridinium iodide (1) as the coupling reagent. 

Carboxamides and sometimes carboxylic esters and carbonitriles are formed as by-products of the alcoholysis. 

Acylation of nitrogen compounds by carboxylic esters. The action of carboxylic esters on ammonia or primary or secondary amines generally leads to carboxamides under relatively mild conditions, and the analogous treatment of carboxylic esters with hydrazine and hydroxylamine provides the most important methods of preparing simple carboxhydrazides and carbohydrox-amic acids. 

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