Ethers halogen-atom substituted

Thus, 4-chloropyridine reacts readily with sodium methoxide at 100°, but 3-chloropyridine is unaffected by these conditions. Further in a number of the tabulated cases of conversions of 2- or 4-halogenopyridines to ethers, halogen atoms at C(3) or G(S) are not replaced. 2,4-, 2,6-or 3,5-Dihalo-genopyridines can undergo mono- or di-substitution according to the conditions used. The qualitative evidence favours slightly the view that substitution at C(4) is easier than at C(2). This is seen in the reaction of 2,4,6-tribromo-pyridine with sodium methoxide, from which 2,6-dibromo-4-methoxy-, 6-bromo-2,4-dimethoxy- or 2,4,6-trimethoxy-pyridine can be obtained, according to the severity of the conditions. This picture is, however, complicated by the reaction of 2,4,6-tribromopyridine with sodium phenoxide, which seems to occur more readily at the a-positions than at the y-position, except in the presence of water . 

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/ ... 

Nucleophilic substitution of halogen atom in aromatic and heteroaromatic halides with a hydroxyamino group proceeds only in substrates that are activated by a strong electron-withdrawing substituent in the benzene ring (e.g. 27, equation 17). Despite this limitation this reaction is useful for synthesis of arylhydroxylamines and usually provides good yields of products. Along with activated aryl halides and sulfonates, activated methyl aryl ethers such as 28 can be used (equation 18). 

Halogen atoms have been placed at C-6 of substituted 6-deoxy-hexoses by a variety of interesting ways, and the products provide potential routes to 6-deoxyhexoses. Helferich and coworkers 4 reported a low yield of methyl 6-chloro-6-deoxy-a-D-glucoside which they prepared by reaction of the (suitably protected) corresponding 6-trityl ether with phosphorus pentachloride. Sinclair 44 has provided a convenient procedure for the preparation of the 6-chloro derivative in yields of 30-35% by allowing methyl a-D-glucopyranoside to react with sulfur monochloride, SjClj, in N,/V-dimethylformamide. A much better yield (73%) of the 6-bromo derivative was reported1 in the reaction of methyl 2,3,4-tri-O-benzoyl-6-O-trityl-a-D-altroside with phosphorus tribromide and bromine. 

Method of Nys and Rekker The Nys and Rekker method [53,54] has been developed for mono- and di-substituted benzenes. The substituents considered are halogen atoms and hydroxyl, ether, amino, nitro, and carboxyl groups, for which contributions have been calculated by multiple regression analysis (s = 0.106, r = 0.994, F = 1405). Rekker discusses the extension of his approach to other compound classes, such as PAHs, pyridines, quinolines, and isoquinolines. 

The war gases belonging to this group may be considered as true ethers whose alkyl groups have a hydrogen substituted by a halogen atom. 

There are numerous investigations of the reactivity of di- and polyhalo-pyridazines, particularly polyfluoropyridazines. Aminolysis of l-phenyl-4,5-dichloropyridazin-6-one has been studied in detail. In this and other reactions with nucleophiles, the halogen atom at position 4 is substituted preferentially, although a mixture of 4-amino and 5-amino derivatives is formed in the reaction between 4,5-dihalopyridazin-6-ones and ammonia or amines. It has been now firmly established that displacement reactions on 3,6-dichloropyridazine 1-oxide with sulfur nucleophiles take place at position 6 in contrast to nitrogen or oxygen nucleophiles, where the 3-chlorine atom is replaced preferentially. In connection with the previously observed self-condensation of 3-chloro-6-methylpyridazine to a tricyclic product, the reaction between 3,6-dichloropyridazine and pyridine N-oxides was investigated. 3,6-Dichloropyridazine with 2-methylpyridine N-oxide at 100°-110°C affords three compounds (171, 172, and 173). With 2,6-dimethylpyridine N-oxide, an ether (174) is also formed. The isolation of... 

The procedure for 1-ethoxy-1-phenylethene is an illustration of a general synthetic method for 1-substituted vinyl ethers, which are not accessible via 1-metalla-tion [9] (compare Chap. IV, Exp. 1). The synthesis starts with the reaction of a Grignard compound with a 1,2-dibromoalkyl ether [231]. A halogen atom in the 1-position of an ether group is very readily replacable, even under non-polar conditions. This reaction is a special case of nucleophilic displacement in which the... 

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