Substitution Reactions with Nucleophilic Reagents

There are a small number of pyryUum reactions that can be categorised as nucleophilic substimtions. 

4-Pyrones react with acetic anhydride at carbonyl oxygen to produce 4-acetoxy-pyryliums, in situ, allowing nucleophilic substitution at C-4 the reaction of 2,6-dimethylpyrone with methyl cyanoacetate is typical. Phosphorus pentachloride likewise converts 4-pyrones into 4-chloropyryliums.  

---

Halogenomethyl, hydroxymethyl and aminomethyl groups readily undergo displacement reactions with nucleophilic reagents. Both side-chain and nuclear substitution products have been obtained (Scheme 57). These two possibilities are exemplified by the reaction of furfuryl chloride with sodium cyanide (Scheme 58). 

Isoxazolin-5-one, 2,3-dimethyl-4-substituted photolysis, 6, 14 Isoxazolinones synthesis, 5, 132 Isoxazolin-3-ones alkylation, 6, 43 synthesis, 6, 106, 129 Isoxazolin-4-ones synthesis, 6, 106-107 Isoxazolin-5-ones alkylation, 6, 39 4,4-dialkyl substituted reaction with Grignard reagents, 6, 40 reactions with bases, 6, 41 synthesis, 6, 103-105 Isoxazolium bisulphate, 2,3,5-trimethyl-hydrogen exchange, 6, 21 Isoxazolium salts deprotonation, 5, 71 as hardeners for gelatin, 1, 363 nucleophilic cleavage, 6, 31 nucleophilic reactions, 6, 28-29 4/f-pyran synthesis from, 3, 761 reactions... 

Reactions with Nucleophilic Reagents In close parallel with the oxidation of tropilidene derivatives by tropylium salts,81 for example, 1,2-dithiolium salts containing a single substituent in position 4 or 5, e.g. 70, can capture a hydride anion from the doubly substituted, highly strained leuco bases (71), thus oxidizing the latter to the more highly substituted and thermodynamically more stable salts (73).82... 

Chemical vapor deposition applications range from the semiconductor-microelectronics industry, to the coatings industry for wear resistance. A significant portion of the precursors are made by nucleophilic substitution reactions with Grignard reagents. The organic... 

III. NUCLEOPHILIC SUBSTITUTION REACTIONS WITH GRIGNARD REAGENTS... 

Nucleophilic Substitution Reactions with Grignard Reagents... 

Two acids with mixed three-membered chains are known, namely selenopentathionic and telluropentathionic acid. They are derived from pentathionic acid by substitution of selenium or tellurium for the middle sulfur atom of the latter, and behave in reactions with nucleophilic reagents as thiosulfates of divalent selenium and tellurium. The first salts of scleno-pentathionic (84) and telluropentathionic (85) acid were isolated in 1949, although the formation reactions in aqueous solutions had been known earlier. Wood (229) has by paper electrophoresis shown that the preparative methods lead to pure products. 

All reactions with nucleophilic reagents mentioned on p 150/151 for thiazole can also be achieved with benzothiazole. Only slight differences are observed. For instance, 2-chlorobenzothiazole reacts about 400 times faster with sodium methoxide or with sodium thiophenolate than 2-chlorothiazole, to give the corresponding substitution products 2-methoxy- and 2-(phenylsulfanyl)benzothiazole. 

Thus, similarly to its substituted homolog 23, borabullvalene 54e exhibits diverse chemoselectivities in its reactions with nucleophilic reagents. Moreover, the main interconverting tautomers (23,52,53 and 56,54e, 59) have essentially the same carbon skeletons, but different relative stabilities. Thus, in the borabullvalene series, the most stable tautomer is 23. This is stipulated by the possibility for the 2p-AO in 23 to conjugate with the ir-system of the double bonds. In the corresponding tautomer (56) of the more strained borabarbaralane series such conjugation is impossible, and borabullvalene 54e is the only observable compound. 

Trifluoropyridines were used for synthesis of substituted 2,5-difluoropyridines. The atom of fluorine which is taking place in the position 2, is most nucleophilic. Therefore, reactions with nucleophilic reagent proceeded highly regioselectively. 3,6-Difluoro-2-methoxypyridine (212) has been obtained from 2,3,6-trifluoropyridine (211) in methanol at presence MeONa [134-136] (Scheme 66). Pyridine (212) was applied in synthesis of antiviral compounds [134]. 

From a number of the reactions to be recorded the substitution products arise from decomposition of initial addition products. From other reactions with nucleophilic reagents, pyridine and its derivatives provide addition rather than substitution products. This is especially so when the group which would be replaced is hydride ion. Because addition compounds may be intermediates in nucleophilic processes generally (p. 218), no attempt is made here to classify separately nucleophilic additions and substitutions. 

The results of ion extraction experiments suggest a possibility that 9 might display a catalytic activity for a nucleophilic substitution reaction with inorganic reagents in organic media. Accordingly, we investigated the catalytic activity of 9c on... 

The reactions of nucleophilic reagents with cationic and uncharged metal carbonyl complexes have received much attention in the past, and it is not surprising that these studies have now been extended to isocyanide metal complexes. Different products in these reactions can arise by three general routes these include ligand substitution, reactions involving attack at a ligand, and reduction of the metal complex. All have been observed in reactions with metal isocyanide complexes. 

Kinetic experiments have been performed on a copper-catalyzed substitution reaction of an alkyl halide, and the reaction rate was found to be first order in the copper salt, the halide, and the Grignard reagent [121]. This was not the case for a silver-catalyzed substitution reaction with a primary bromide, in which the reaction was found to be zero order in Grignard reagents [122]. A radical mechanism might be operative in the case of the silver-catalyzed reaction, whereas a nucleophilic substitution mechanism is suggested in the copper-catalyzed reaction [122]. The same behavior was also observed in the stoichiometric conjugate addition (Sect. 10.2.1) [30]. 

---