2-chloro nucleophilic displacement

H-Pyrimido[l, 2-6]pyridazin-2-one, chloro-nucleophilic displacement reactions, 3, 343 2H-Pyrimido[l,2-6]pyridazin-2-one, 7-chloro-synthesis, 3, 354... 

Silacyclopentadiene, 1,1 -dimethyl-2,3,4,5-tetraphenyl-irradiation, 1, 618 structure, 1, 617 Silacyclopentadiene, 1-methyl-synthesis, 1, 615 Silacyclopentadienes Diels-Alder reactions, 1, 618 reactions, 1, 617-620 reduction, 1, 617 structure, 1, 616 synthesis, 1, 585, 586, 614-616 Silacyclopentane, 1-chloro-nucleophilic displacement, 1, 608 Silacyclopentanes, 1, 605-609 chemical properties, 1, 607-608 synthesis, 1, 605-607... 

Substitution reactions on dialkyl peroxides without concurrent peroxide cleavage have been reported, eg, the nitration of dicumyl peroxide (44), and the chlorination of di-/ fZ-butyl peroxide (77). Bromination by nucleophilic displacement on a-chloro- or a-hydroxyalkyl peroxides with hydrogen bromide produces a-bromoalkyl peroxides (78). 

Halogen atoms on benzazole rings can be activated toward nucleophilic displacement by electron-withdrawing groups. Thus azide ion displaces chlorine from 5-chloro-4-nitro- and 4-chloro-7-nitro-benzofuroxan (65JCS5958). 

Chloro-5-arylisoxazoles undergo nucleophilic displacement with alkoxide ion. Halogen atoms in the 5-position of the isoxazole nucleus are readily displaced if an activating group is present in the 4-position (63AHC(2)365). 

Several examples of nucleophilic displacement of nitro-activated leaving groups have been recorded. 5,6-Dinitrobenzofuroxan with aniline and p-bromoandine gives the corresponding substitution product (50). Azide ion displaces chloride from both 5-chloro-4-nitro- and 4-chloro-7-nitrobenzofuroxan (51 and 52) the product from the former loses nitrogen spontaneously to give furoxanobenzo-furoxan (benzobisfuroxan, 17), which is also formed, although in poor... 

It is often advantageous to proceed to a desired product through two nucleophilic displacements rather than directly when one can exploit a difference in the reactivity of two leaving groups. An example is the conversion of 4-chloro-2,6-dimethoxypyrimidine (109) (not satisfactorily reactive with sulfanilamide anion) by means of trimethylamine into the more reactive trimethylammonio derivative 110. Conversion of chloro-quinohnes and -pyrimi-dines into nitriles is best accomplished by conversion (with sulfite) into the sulfonic acids before reaction with cyanide. 

Ring closure of 2-chloro-l-phenethylpyridinium ion (247) (prepared in situ) to l,2-dihydro-3,4-benzoquinolizium ion involves intramolecular nucleophilic displacement of the chloro group by the phenyl 77-electrons. A related intermolecular reaction involving a more activated pyridine ring and more nucleophilic 7r-electrons is the formation of 4-( -dimethylaminophenyl)pyridine (and benzaldehyde) from dimethylaniline and 1-benzoylpyridinium chloride (cf. Section III,B,4,c). 

Because of the ease of ring synthesis, symmetrically trisubstituted s-triazines have been more thoroughly studied, but a few nucleophilic substitutions of derivatives bearing a single leaving group are known. 2-Chloro-4,6-diphenyl- and 2-chloro-4,6-dimethyl-s-triazines (318) undergo facile nucleophilic displacements with ammonia, amines, and hydrazine, with alkoxide, or with hydrosulfide... 

OKO-l,3,7-triazanaphthalene (450) forms acyloxy derivatives in situ with phosphorus oxychloride and pentasulfide which undergo nucleophilic displacement with chloride ion and with a complex sulfide ion, respectively, to form the 4-chloro and 4-thioxo derivatives. The 4-carboxymethylthio compoimd failed to undergo the ring-opening reaction (see below) characteristic of more activated azino- and diazino-pyrimidines, but it did yield about 10% of the 4-0X0 displacement product. 

Ring expansions of 3-aryl-7-azido-2-chloroquinolines, e.g. 21, in potassium methoxide-meth-anol/dioxane yield mixtures of the expected 3-aryl-2-chloro-7-methoxy-9//-pyrido[2,3-f]pyrid-ines, e.g. 22, and the 2,7-dimethoxy derivatives, e.g. 23, formed by nucleophilic displacement of the 2-chloro group.154 ... 

Benzofurazan (benz-1,2,5-oxadiazole) reacted with bromine by addition to give a4,5,6,7-tetrabromo adduct. Bromine in hydrobromic acid solution 4-brominated both 5-methyl- and 5-bromo-benzofurazans (74JHC8I3). When 4,7-dinitrobenzofurazan was treated with ammonium chloride in refluxing acetic acid, nucleophilic displacement gave rise to the 4-chloro-7-nitro derivative (83URP1004375). Naphtho[l, 2-c]furazans (42) are mainly 4-halogenated, but there is minor substitution in the 8-position (73CHE1331). 

Nucleophilic halogenations tend to favor the pyridine moiety. The Meisenheimer reaction of thieno[3,2-6]pyridine N-oxide (125) gave only a 24% yield of a 1.4 1 mixture of the 5- and 7-chloro derivatives. Nucleophilic displacement of a 7-nitro group provided a more satisfactory route to the 7-chloro (73%) and 7-bromo (39%) derivatives (85JHC1249). 

Both 5- and 7-amino derivatives of 133 were diazotized and converted into the chloro derivatives using concentrated hydrochloric acid with or without copper(I) chloride (72RTC650 78JHC839). Similarly prepared from 4-aminoimidazo[4,5-c]pyridine was the 4-chloro derivative (65JMC708). A nitro group in the 4-position of 134 was particularly susceptible to nucleophilic displacement by halide (74CHE744). 

Bordwell and Cooper211 drew attention to the inertness of a-halosulfones and related compounds towards nucleophilic displacements of the halogen. Thus chloromethyl p-tolyl sulfone reacts with potassium iodide in acetone at less than one-fiftieth of the rate for n-butyl chloride. On the other hand, l-(p-toluenesulfonyl)-3-chloro-l-propene reacts about 14 times faster than allyl chloride. This contrast (and other comparisons) led the authors to attribute the inertness of a-halosulfones to steric hindrance, which was eliminated when the sulfonyl group was more remote from the reaction center. 

Chloro-3-methyl-6-nitroquinoxaline (96, R = Cl) gave 2-hydrazino-3-methyl-6-nitroquinoxaline (96, R = NHNH2) (H2NNH2 H2O, EtOH, 20°C, lh >95% H2NNH2 H2O, EtOH, reflux, 3h 60% the second of these procedures appears to be a classical example of overkill in nucleophilic displacement that results in a lower yield). 

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