Brominated esters

To a stirred mixture of 20.8 gm (0.25 mole) of pyridine and 40.5 gm (0.25 mole) of ethyl orthoacetate is added dropwise 40 gm (0.25 mole) of bromine over a period of hr while the temperature is kept at 10°C. The pale yellow brominated ester is filtered, the pyridine hydrobromide washed with ether, the ether washings combined with the bromo ester and then distilled to afford 44 gm (74 %), b.p. 77°-79°C (9 mm), ng 1.4393, d 1.2639. A small amount of ethyl orthodibromoacetate, b.p. 102°-104°C (8 mm), 1.469, d 1.5272, is also isolated. 

The mechanism in Figure 12.7 implies that the stoichiometric use of phosphorus tribromide in the second variant of the Hell-Volhard-Zelinsky bromination leads to the selective formation of the a-bromocarboxylic acid bromide (Formula B in Figure 12.8). Often these compounds are hydrolyzed to give the bromocarboxylic acids C. More importantly, a-bromocarboxylic acid bromides B can also undergo alcoholysis and in this way provide access to a-brominated esters D. 

Though some of these reactions use enolisable aldehydes, none uses enolisable Michael acceptors so the question of competition of this a reaction with extended enolisation proper has not arisen. One alternative approach uses an indium-mediated reaction of the y-brominated ester 163 with aldehydes to give either non-conjugated 165 or conjugated 166 a -products.43... 

Brominated esters of benzoic acids were obtained, which have the following strac-... 

Other types of functionalized poly(3-alkylthiophene)s can be prepared in order to obtain polymeric materials with different chemical, optical, and electronic properties and different solubilities. The organozinc route has been used to synthesize poly thiophenes bearing a phosphonic ester functionality or functional groups such as bromine, ester, alcohol, and acetal-protected aldehyde as terminal groups of C-3-substituents, as illustrated in Scheme 11 [76]. 

Substitution chemistry remains one of the most popular and simplest approaches to the formation of nitrogen-carbon(sp ) bonds. An example of this method involved the addition of pyrimidines to brominated esters (Scheme 3.1) [1]. The first step in this sequence was the protection of the primary amine in order to direct the reaction to the N l)-H of the pyrimidine. Once the protection was complete, addition of a strong base deprotonated the N l)-H and generated the amide that attacked the brominated ester to generate the new nitrogen-carbon(spO bond. 

Lectka has developed a number of innovative strategies for the enantioselective transformation of ketenes by activation with chiral amines [27, 129). In the presence of cinchona alkaloid catalyst 237 and base, acid chloride 236 is converted into zwitterion 238 (Scheme 3.35). These intermediates behave effectively as chiral enolates and partake in electrophilic chlorination and bromination reactions [130-132]. Upon treatment with brominating agent 239, the depicted brominated ester 240 was obtained in 68% yield and 98% optical purity [131],... 

Quite surprisingly V. aerophoba failed to incorporate radioactivity from [U- " C]-L-tyrosine into aerothionin (7), aeroplysinin-1 (4) and the dienone (1) inactive aerothionin was also isolated when the animals were fed with [U- " C]-L-ornithine (71). However the sponges utilized these aminoacids for the synthesis of fatty acids. A very slow rate of biosynthesis might account for these results. A dietary origin for these compounds can be also suspected in this connection the recent report of the isolation of the brominated esters (19) and (20) (after methylation) from hydrolyzed extracts of the red alga Halopytis incurvus (41) seems relevant. 

Unsaturated esters decolourise a solution of bromine in carbon tetrachloride and also neutral potassium permanganate solution. 

Ethyl a-bromopropionate. This preparation illustrates the facile bromination of an acid chloride (propionyl chloride) in the presence of red phosphorus, and the subsequent conversion of the bromoacid chloride into the ethyl ester by direct interaction with ethanol. 

The bromine adds on at the ethylenic linkage to form thedibromo compound (I), which easily loses hydrogen bromide to give the mono-bromo keto ester (II) ... 

Unsymmetrically substituted dipyrromethanes are obtained from n-unsubstitued pyrroles and fl(-(bromomethyl)pyiToIes in hot acetic acid within a few minutes. These reaction conditions are relatively mild and the o-unsubstituted pyrrole may even bear an electron withdrawing carboxylic ester function. It is still sufficiently nucleophilic to substitute bromine or acetoxy groups on an a-pyrrolic methyl group. Hetero atoms in this position are extremely reactive leaving groups since the a-pyrrolylmethenium( = azafulvenium ) cation formed as an intermediate is highly resonance-stabilized. 

Difluoroacetic acid undergoes reactions typical of a carboxylic acid such as forming an ester when heated with an alcohol and sulfuric acid. Typical esters are methyl difluoroacetate [433-53-4], bp, 85.2°C, and ethyl difluoroacetate [454-31-9], bp, 99.2°C. It can also be photochemicaHy chlorinated to chlorodifluoroacetic acid [76-04-0] or brominated in the presence of iron to bromodifluoroacetic acid [667-27-6] (37,38). 

An alternative synthesis of (Z)-l-halo-l-alkenes involves hydroboration of 1-halo-l-alkynes, followed by protonolysis (246,247). Disubstituted ( )-and (Z)-a1keny1 bromides can be prepared from ( )- and (Z)-a1keny1 boronic esters, respectively, by treatment with bromine followed by base (248). 

Another problem arises from brominated aromatic species derived from inorganic bromides used as oxidation cocatalysts. As a result, the cmde NDA is converted to its dimethyl ester, DMNDA [840-65-3] and solvent recrystalHzed to give a high purity diester (36—38). A process for purifying NDA directly by hydrogenation (pure TA process) has also been described (39). 

Acids and esters (see Esters, organic) are less easily brominated than aldehydes or ketones. Acid chlorides and anhydrides are more easily brominated (23). 

Aldehydes can be dkeedy converted to esters using bromine in alcohol solvents with sodium bicarbonate buffer (41). 

Methyl bromide slowly hydrolyzes in water, forming methanol and hydrobromic acid. The bromine atom of methyl bromide is an excellent leaving group in nucleophilic substitution reactions and is displaced by a variety of nucleophiles. Thus methyl bromide is useful in a variety of methylation reactions, such as the syntheses of ethers, sulfides, esters, and amines. Tertiary amines are methylated by methyl bromide to form quaternary ammonium bromides, some of which are active as microbicides. 

In the pyrrole series, ester groups a to nitrogen are more readily hydrolyzed by alkali, but those in a /3 position more readily by acid. A methoxycarbonyl group in the 2-positlon is meta directing thus bromination yields mainly 4-bromo-2-methoxycarbonylpyrrole. Free radical chlorination with f-butylhypochlorite gives the 5-chloro derivative. 

Benzo[b]furan-2-carboxylic acids bromination, 4, 602 chloromethylation, 4, 602 from coumarins, 3, 686 IR spectra, 4, 590 methyl ester... 

Furan-2-carbonyl chloride, 5-alkyl-3,4-dichloro-synthesis, 4, 690 Furancarboxamides rotational isomerism, 4, 543 Furan-2-carboxylic acid, 5-acetylamino-ethyl ester reactions, 4, 647 Furan-2-carboxylic acid, amino-properties, 4, 708 Furan-2-carboxylic acid, 5-bromo-nitration, 4, 603, 711 Furan-2-carboxylic acid, 3-methyl-methyl ester bromination, 4, 604 Furan-2-carboxylic acid, 5-methyl-nitration, 4, 602... 

Furan-3-carboxylic acid, 2-methyl-methyl ester bromination, 4, 604 synthesis, 4, 686 Furancarboxylic acids acidity, 4, 71... 

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