Esters halogen-atom substituted

The nucleophilic substitution of a halogen atom at C-5 in the isoxazole nucleus without further functional substituents is so far unknown, but recently reports appeared on the nucleophilic substitution reactions at C-5 in isoxazole derivatives with benzoyl (78 79), ester, and cyano groups (81—>80, 82) in the 4-position. ... 

Nucleophilic substitution of the halogen atom of halogenomethylisoxazoles proceeds readily this reaction does not differ essentially from that of benzyl halides. One should note the successful hydrolysis of 4-chloromethyl- and 4-(chlorobenzyl)-isoxazoles by freshly precipitated lead oxide, a reagent seldom used in organic chemistry. Other halides, ethers, and esters of the isoxazole series have been obtained from 3- and 4-halogenomethylisoxazoles, and 3-chloro-methylisoxazole has been reported in the Arbuzov rearrangement. Panizzi has used dichloromethylisoxazole derivatives to synthesize isoxazole-3- and isoxazole-5-aldehydes/ ... 

Chlorination or bromination of isothiochroman yields the corresponding 1-halo derivatives,241,252 253 which are intermediates for numerous isothiochromans since the halogen atoms are benzylic and, therefore, very susceptible to nucleophilic substitution. Thus, 1-chloroisothio-chroman wth mercuric cyanide gives the 1-cyano derivative, which provides the 1-carboxylic acid, 1-ester, and the 1-amide.239,252 The remaining 1-H of the 1-cyano derivative is acidic and, with base,... 

The Labile Nature of the Halogen Atom in Organic Compounds. Part V. The Action of Hydrazine on the Halogen Derivatives of Some Esters and Substituted cycloHexanes, E. L. Hirst and A. K. Macbeth,]. Chem. Soc., 121, 2169 (1922). 

A variety of bases have been used to effect dehydrohalogenation of halo acids and halo esters. a-Bromo esters or a-bromo acyl halides give a,/3 lefinic acids with alcoholic potassium hydroxide. Yields are poor with the higher-molecular-weigbt a-bromo acids other products are those formed by substitution of the halogen atom by the basic anions. 

Functionalized P-amino-a, -unsaturated lactones, esters and nitriles can be prepared by nucleophilic vinylic substitution of halogen atoms by amines on the corresponding 3-halo-a,3-unsaturated compounds (12), (13) and (15) (Scheme 9). 3-Bromo-2-butenoates ( )-(13) and (Z)-(13) reacted with secondary amines to give ( )-p-aminopropenoates ( )-(14) regardless of the initial stereochemistry, while the reaction with primary amines yielded a mixture of ( )- and (Z)-(14), when R = H, with the latter predominant. In contrast, the substitution of ( )- and (Z)-nitriles, ( )-(15) and (Z)-(15), with second-... 

Direct substitution of F for OH by means of HF has no preparative importance. All the methods of preparing alkyl fluorides from alcohols proceed in principle by way of esters the alcohol is converted into the alkyl chloride, bromide, iodide, or / -toluenesulfonate, and then the halogen atom (see page 204) or the tosyloxy group (see page 229) is replaced by fluorine. 

The reaction of a-halo esters with carbonyl compounds in the presence of sodium ethoxide leads to 2-(ethoxycarbonyl)oxiranes (Darzens 1904). They are known as glycidic esters. In the first step, the a-halo ester is deprotonated by the base to the corresponding carbanion. This nucleophile adds to the carbonyl compound in a rate-determining step. Finally, the halogen atom is intramolecularly substituted, e.g. ... 

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