Preparation esters from carboxylic acid

Further examples of the preparation and cleavage of benzyl esters are Included in section 107 (Esters from Carboxylic Acids) and section 23 (Carboxylic Acids from Esters)... 

The most widely used method for the preparation of carboxylic acids is ester hydrolysis. The esters are generally prepared by heterocyclization (cf. Chapter II), the most useful and versatile of which is the Hantzsch s synthesis, that is the condensation of an halogenated a- or /3 keto ester with a thioamide (1-20). For example ethyl 4-thiazole carboxylate (3) was prepared by Jones et al. from ethyl a-bromoacetoacetate (1) and thioformamide (2) (1). Hydrolysis of the ester with potassium hydroxide gave the corresponding acid (4) after acidification (Scheme 1). 

Section 15.3 Alcohols can be prepared from carbonyl compounds by reduction of carboxylic acids and esters. See Table 15.3. 

Linearly annelated 3-phenyl-3//-5-ethyl-8-oxo-5,8-dihydrotriazolo[4,5-g]quin-oline-7-carboxylic acid and ester 173 were prepared starting from ethyl 7-chloro-6-... 

The 3-o-ch orophenvl-5-methvlisoxa2ole4-carboxylic acid, from which the acid chloride was prepared, was obtained by hydrolysis of the ester product of the reaction between o-chloro-benzohydroxamic chlorideand ethyl acetoacetate in methanolic sodium methoxide. Reaction with thionyl chloride gave the starting material. 

A series of C-nucleoside analogs of type 1.5 were prepared from the reaction of 1-bromodeoxyheptulose derivatives with 3-arylamino-2-cyano-3-mercaptoacrylic acid ethyl ester, 3-amino-5-thioxopyrazolin-4-carboxylic acid ethyl ester, and 2-amino-4-thioxo-4,5-dihydro-l//-benzo[b][l,4]-diazepin-3-carboxylic acid ethyl ester (86PHA548). 

Halogenations with dihalotriphenylphosphoranes have been reviewed briefly by Fieser and Fieser.4 Dibromotriphenylphos-phorane appears to have been studied somewhat more than the dichloro compound, but both reagents effectively convert alcohols to alkyl halides, carboxylic acids and esters to acid halides, etc. The reaction of 1,2-epoxycyclohexane with dibromotriphenylphos-phorane under conditions similar to those described here gives a mixture of cis- and trans-1,2-dibromocyclohexanes. A reagent prepared from triphenylphosphine and carbon tetrachloride has been used for similar transformations.5... 

Acyl cations are now well-established chemical species. They can be prepared in quantity in solution, and several have been isolated as their crystalline salts. Recent papers have described their formation from carboxylic acids and esters under strongly acidic conditions81214, but they are most conveniently available from the reactions of acyl halides with L.ewis acids21 well-defined Lewis acid-base complexes are formed, which decompose in a second stage to the acyl cations21-23, viz. 

As a class of compounds, nitriles have broad commercial utility that includes their use as solvents, feedstocks, pharmaceuticals, catalysts, and pesticides. The versatile reactivity of organ onitriles arises both from die reactivity of the C=N bond, and from die ability of the cyano substituent to activate adjacent bonds, especially C-H bonds. Nitriles can be used to prepare amines, amides, amidines, carboxylic acids and esters, aldehydes, ketones, large-ring cyclic ketones, imines,... 

The generation of radicals from carboxylate ions at the anode (Section 2.17.6, p. 115), and their coupling to form new carbon-carbon bonds is illustrated by the synthesis of hexacosane (Expt 5.11). The method has been usefully applied to the preparation of esters of long-chain carboxylic acids, from which of course the free acids may be prepared by hydrolysis. 

Here, we report the application of this procedure for immobilizing Mucor miehei lipase. A catalytic test was aimed at producing esters by direct esterification reactions with a large range of carboxylic acids (from C4 to C16), and a diversity of alcohols (from C4 to C8). Several reaction model systems are analyzed in order to illustrate the kind of products that can be made by using an experimental preparation of lipase immobilized on POS-PVA particles. 

A solution is prepared from 3.3 g (8.5 mmol) of 6-benzyloxy-4-methoxymethyl-l,2,3,4-tetrahydro-p-carboline-3-carboxylic acid isopropyl ester in 150 ml of methylene chloride, combined under argon with 3.9 ml of triethylamine, and cooled to -15°C. At this temperature, a solution of 3.2 ml (25.6 mmol) of t-butyl hypochlorite in 50 ml of methylene chloride is added dropwise without delay to this solution. After the adding step is completed, the mixture is stirred for another 10 min, combined with 2.6 ml of triethylamine, and agitated for 2 hours at room temperature. Subsequently, the mixture is concentrated to one-half thereof and extracted once by shaking with dilute ammonia solution. The organic phase is dried, filtered, and concentrated. The residue is chromatographed over silica gel with methylene chloride acetone=4 l as the eluent. Recrystallization from ethyl acetate gives 1.1 g (35% yield) of 6-benzyloxy-4-methoxymethyl-p-carboline-3-carboxylic acid isopropyl ester, m.p. 150-151°C. 

Chiral homoallylamines are valuable synthons for the preparation of biologically active components including P-amino carboxylic acids or esters, obtained by oxidation of the ally lie functionality.1-29 Because removal of the chiral auxiliary by hydrogenation leads to the loss of the allylic functionality, we developed alternative routes for the conversion of the adduct into the unprotected homoallylamines. As a typical example, (f ,f )-PGA-homoallylamine derived from isobutyraldehyde Hi was used to develop the so-called mroStrecker and the decarbonylation method for the conversion of (R)-phenylglycine amide protected homoallylamines into /V-benzylidene protected homoallylamines 15 (Scheme 25.7). 

Acyl radicals are very useful synthetic intermediates. Their preparation is not simple since the corresponding halides are highly electrophilic and cannot be used as radical precursors. Organocobalt compounds were proposed as suitable source of acyl radicals [44]. However, the use of acyl selenides proved to be more general [45, 46]. These radical precursors can be efficiently prepared from the corresponding carboxylic acids and esters [47]. Acyl phenyl selenides should be preferred, when possible, relative to acyl methyl selenides due to the consumption of two equivalents of tin hydride with this last system (Scheme 1) [4]. Acyl selenides have found many applications in tandem radical additions to alkenes. Examples of intermole-cular [Eq. (18)] [48,49] and intramolecular reactions [Eq. (19)] [50a] are reported. The enoyl selenide 68 give the unsaturated acyl radicals 69. This intermediate... 

The usual range of carboxylic acid derivatives can be prepared and interconverted. Both carboxylic acid and ester functions are capable of reduction by lithium aluminum hydride to alcohols, or by controlled potential reduction to aldehydes. Attempts to form the anhydride from imidazole-4,5-dicarboxylic acid by heating with acetic anhydride failed. Instead, compound (199) is formed. This product forms the monoester (200) when heated with methanol and the hydrazide (201) when treated similarly with hydrazine (Scheme 107) (75S162). The corresponding l-methyl-4,5-dicarboxylic acid loses the 4-carboxyl group when heated with acetic anhydride, but in boiling aniline it is transformed into the 1-methyl-4-carboxanilide (79H(12)186). 

Table 8 Examples of 3-Alkyl- and 3-Aryl-[l,2,4]triazolo[4,3-a]pyridines Prepared from 2-Hydrazinopyridines and Carboxylic Acids, Anhydrides, Esters or Ortho Esters <66JOC25i, 78JHC439.7OJHC703,70JHC1019)...

Difluoroimidazole 1571 has been prepared from 5-fluoroimidazole-4-carboxylic acid ethyl ester 1568. The ester 1586 is converted into the carbonyl azide 1569, which undergoes Curtius rearrangement in tert-huVf alcohol to produce 4-/-butyloxycarbonylamino-5-fluoroimidazole 1570. In situ diazotization of the resulting amine and irradiation produces 4,5-difluoroimidazole 1571 (Scheme 405) <2001JFC(107)147>. 

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