Nucleophilic aromatic fluoride

The range of nueleophiles whieh have been observed to partieipate in nueleophilie aromatie substitution is similar to that for S[, 2 reactions and includes alkoxides, phenoxides, sulftdes, fluoride ion, and amines. Substitutions by earbanions are somewhat less common. This may be because there are frequently complications resulting from eleetron-transfer proeesses with nitroaromatics. Solvent effects on nucleophilic aromatic substitutions are similar to those discussed for S 2 reactions. Dipolar... 

The ease of dehalogenation of C H X by Ni(ll)/ IMes HCl 1/NaO Pr decreased in the order 1 > Br > Cl F. Subsequent work showed that a 1 1 combination of Ni and NHC in the presence of NaOCHEt resulted in enhanced reactivity towards aryl fluorides [6], Again, the A-mesityl substituted ligand IMes HCl 1 imparted the highest level of catalytic activity. Table 8.2 illustrates that hydrodefluorination is sensitive to both the nature of the substituents on the aromatic ring and the specific regioisomer. Thus, 2- or 4-fluorotoluene (Table 8.2, entry 2) proceeded to only 30% conversion after 15 h, whereas quantitative conversion of 2-fluoroanisole (Table 8.2, entry 3) and high conversion of 3-fluoropyridine (Table 8.2, entry 5) was achieved in only 2-3.5 h. The reactivity of 2-fluoropyridine was compromised by more efficient nucleophilic aromatic substitution. 

With the nitro group successfully introduced, the aromatic fluoride substituent in 11 was ready to undergo the nucleophilic aromatic substitution with the hydrox-ypyridine 9. The reaction proceeded smoothly in DMF at 55 °C using an equimolar amount of cesium carbonate as the base and provided a 90% isolated yield of 23 after crystallization. With compound 23 in hand, only the reduction of the nitro... 

A one-pot three-step conversion of aryl fluorides to phenols based on a consecutive nucleophilic aromatic substitution/isomerization/hydrolysis sequence has been reported by Levin and Du (Scheme 6.126) [256], The authors discovered that 2-butyn-l-ol can function as a hydroxyl synthon through consecutive SNAr displacement, in situ isomerization to the allenyl ether, and subsequent hydrolysis, to afford phenols rapidly and in good yields. In most cases, excesses of 2-butyn-l-ol (1-2 equivalents) and potassium tert-butoxidc (2-4 equivalents) were required in order to achieve optimum yields. 

NUCLEOPHILIC AROMATIC SUBSTITUTION OF ARYL FLUORIDES BY SECONDARY NITRILES PREPARATION OF 2-(2-METHOXYPHENYL)-2-METHYLPROPIONITRILE... 

Tertiary benzylic nitriles are useful synthetic intermediates, and have been used for the preparation of amidines, lactones, primary amines, pyridines, aldehydes, carboxylic acids, and esters. The general synthetic pathway to this class of compounds relies on the displacement of an activated benzylic alcohol or benzylic halide with a cyanide source followed by double alkylation under basic conditions. For instance, 2-(2-methoxyphenyl)-2-methylpropionitrile has been prepared by methylation of (2-methoxyphenyl)acetonitrile using sodium amide and iodomethane. In the course of the preparation of a drug candidate, the submitters discovered that the nucleophilic aromatic substitution of aryl fluorides with the anion of a secondary nitrile is an effective method for the preparation of these compounds. The reaction was studied using isobutyronitrile and 2-fluoroanisole. The submitters first showed that KHMDS was the superior base for the process when carried out in either THF or toluene (Table I). For example, they found that the preparation of 2-(2-methoxyphenyl)-2-methylpropionitrile could be accomplished h... 

G. Angelini, M. Speranza, A.P. Wolf, C.Y. Shiue, Nucleophilic aromatic-substitution of activated cationic groups by F-18-labeled fluoride—A useful route to no-carrier-added (nca) F-18-labeled aryl fluorides, J. Fluor. Chem. 27 (1985) 177-191. 

Schnur and co-workers " summarized typical reactions that can be performed on functional groups of substituted 2,4-oxazolidinediones without ring opening. These reactions include reduction with iron-acetic acid, chlorosulfonation, nucleophilic displacements of aromatic fluorides, and acid hydrolysis with HCl/formic acid. Nonetheless, there are examples of useful ring cleavage reactions involving 2,4-oxazolidinediones. 

K18F has been used to prepare 18F-labeIled aromatic fluorides by nucleophilic substitution on activated aromatic halides.88,90... 

Reaction of a nitro-substituted aryl halide with a good nucleophile leads to nucleophilic aromatic substitution. Methoxide will displace fluoride from the ring, preferentially at the positions ortho and... 

Indications of the occurrence of cycloaddition were first obtained from reactions of specifically deuterated allyl anions with tetrafluoroethylene. Assuming that no hydrogen/deuterium exchange occurs in the collision complex as shown for the allyl anions themselves (Dawson el al., 1979a), the results obtained (Nibbering, 1979) may be interpreted as indicating that 65% of the allyl anions react by a linear addition (51), 20% by a [2 + 2] atom cycloaddition (52) and 15% by a [2 + 3] atom cycloaddition. (53). It should be noted here that the precise mechanistic details of the losses of HF molecules from the collision complexes in eqns (51)—(53) are not known. However, in view of the nucleophilic aromatic substitution discussed in the previous section, it is quite likely that they occur in a stepwise fashion in which complexes solvated by fluoride anions play a role. 

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