Nucleophilic displacements of leaving

The 2-alkyl anion derived from 2,5-dimethylthiadiazole (53) and sodium hydride adds to the annular carbon of (53) to give (54) <89CZ217>. Examples of nucleophilic displacement of leaving groups from the 2- and 5-positions of thiadiazoles are discussed in Section 4.10.8. 

The imidazo[l,5-a]pyridine ring system has been successfully functionalized with various electrophilic reagents, metalated, and reduced in one case. No nucleophilic displacements of leaving groups have been reported on appropriate derivatives. 

Nucleophilic displacement of leaving groups can also be carried out in suitable cases, for example, of the 4-methylthio in 3-cyano-2-pyrones. ... 

In addition to the nucleophilic substitution of hydride atom from quinolines and isoquinolines, a reaction of high value for introduction of variety of substituents is the nucleophilic displacement of leaving groups on the heterocycle. As an example, 4-chloro-8-trifluoromethylquinoline reacts in a nucleophilic displacement of chlorine atom with methyl anthranilate, to provide the precursor of NS AID antihacterial flocatfenine. ... 

Alkali metal (K, Na) [ CJcyanides have been extensively employed in the formation of alkyl [ CJnitriles via nucleophilic displacement of leaving groups such as primary halides, sulfonates and trialkylammonium salts in examples too numerous to mention. In special cases (e.g., 1) other leaving groups have been used, such as benzotriazol-l-yl. The most important considerations in the choice of leaving group are often the ease of substrate preparation and the compatibility of the displacement reaction with substrate ancillary functional groups. 

The preparation of esters can be classified into two main categories (1) carboxy-late activation with a good leaving group and (2) nucleophilic displacement of a caiboxylate on an alkyl halide or sulfonate. The latter approach is generally not suitable for the preparation of esters if the halide or tosylate is sterically hindered, but there has been some success with simple secondaiy halides and tosylates (ROTs, DMF, K2CO3, 69-93% yield). ... 

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... 

The final step is the nucleophilic displacement of the oxyphosphonium group by the carboxylate anion via a SN2-mechanism, yielding ester 3 with inverted configuration at the stereogenic center, and triphenylphosphine oxide. A hydrolysis of the ester 3 will leave the new configuration unchanged, and yield the inverted alcohol 4 ... 

Nucleophilic displacement of spP-carbon bonded halide and related leaving groups... 

TABLE 4. Sulfones from nucleophilic displacement of different weak leaving groups by sulfinates R1 SO2M... 

Nucleophilic substitution of leaving groups is probably the most important area in pyrimidine reactivity and, in particular, the differential reactivity of C-2 and C-4 is the most investigated topic. The displacement of 2- and 4-sulfide and sulfone groups is referred to in the synthesis section. The selective hydrolysis of 4-amino-2-chloropyrimidines under acidic conditions has been studied in great detail by a process research group <06OPRD921>. 

As we have already mentioned, nucleophilic displacements of ring C-substituents in 1,3,4-oxadiazoles are seldom reported. The reactions occur only for compounds containing very good leaving groups, as shown in Scheme 12 <2001JA6179, 2004MI1343>. 

Direct nucleophilic displacements of the phosphate leaving group in inert organic solvents by nucleophiles of the... 

Studies of gas-phase S"n2 reactions at sp carbon have been made by Fourier transform ion cyclotron resonance mass spectrometry (FTlCRMS) and complemented by both semiempirical and ab initio MO calculations. The particular processes of interest involved intramolecular reactions in which neutral nucleophiles displace neutral leaving groups within cationic substrates, e.g. A-(2-piperidinoethyl)-2,4,6-triphenylpyridinium cation (59), in which the piperidino moiety is the nucleophile and 2,4,6-triphenylpyridine (60) is the leaving group. No evidence has been obtained for any intermolecular gas-phase 5) 2 reaction involving a pyridine moiety as a leaving group. The quantum mechanical treatments account for the intramolecular preference. 

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