Electrophilic reactions alkylation

The 1,3-diaLkylirnidazolium ylides 14 thus generated exhibit the behavior of nucleophilic carbenes according to their electron distribution. For instance, they undergo electrophilic reactions (alkylation, acylation, halogenation, etc.) at C-2 [380] a recent example is the amidoalkylation of imidazolium yhdes [381]. 

This realization led me to study related possible intermolecular electrophilic reactions of saturated hydrocarbons, Not only protolytic reactions but also a broad scope of reactions with varied electrophiles (alkylation, formylation, nitration, halogenation, oxygenation, etc.) were found to be feasible when using snperacidic, low-nucleophilicity reaction conditions. 

Diazepines alkylation, 7, 617 electrophilic reactions, 7, 615 with fused heterocyclic rings... 

Pyrimidin-5-amine, 4-methylamino-synthesis, 3, 121 Pyrimidin-5-amine, 4-oxo-purfne synthesis from, 5, 582 Pyrimidinamines acylation, 3, 85 alkylation, 3, 86 basic pXa, 3, 60-61 diazotization, 3, 85 Dimroth rearrangement, 3, 86 electrophilic reactions, 3, 68 Frankland-Kolbe synthesis, 3, 116 hydrolysis, 3, 84 IR spectra, 3, 64 N NMR, 3, 64 nitration, 3, 69 Principal Synthesis, 3, 129 reactivity, 3, 84-88 structure, 3, 67 synthesis, 3, 129 Pyrimidin-2-amines alkylation, 3, 61, 86 basic pK , 3, 60 diazotization, 3, 85 hydrogenation, 3, 75 hydrolysis, 3, 84 mass spectra, 3, 66 Pyrimidin-4-amines acidity, S, 310 alkylation, 3, 61, 86 basic pXa, 3, 61 Schifi base, 3, 85 synthesis, 3, 110, 114 1,3,5-triazines from, 3, 518 Pyrimidin-5-amines basic pXj, 3, 61 hydrogenation, 3, 75 reactions... 

Pyrimidine-4(3H)-thione, 6-methoxy-5-nitro-reduction, 3, 88 Pyrimidinethiones acidic pK, 3, 60 S-acylation, 3, 95 N-alkylated synthesis, 3, 139 aminolysis, 3, 94 desulfurization, 3, 93 electrophilic reactions, 3, 69 hydrolysis, 3, 94 oxidation, 3, 94, 138 pyrimidinone synthesis from, 3, 133 reactions... 

Thiadiazoloazines fused, 6, 711-748 alkyl side-chain activation, 6, 740 bond lengths, 6, 731 electrophilic reactions, 6, 735, 736 H NMR, 6, 731 IR spectra, 6, 732 mass spectra, 6, 732... 

Unsaturated fluorocarbons are much more reactive toward nucleophiles than then hydrocarbon counterparts owing to fluorme s ability to both stabihze carban ions and mductively increase the electrophihcity of multiple bonds and aromatic nngs Nucleophihc attack dominates the chemistry of unsaturated fluorocarbons, and the role of fluonde ion in fluorocarbon chemistry is analogous to that of the proton in hydrocarbon chemistry [129] Like the related electrophilic reactions for hydrocarbons, there are fluonde-promoted isomenzations and dimenzations (equation 9), oligomenzations (equation 10), additions (equation 11), and amomc Fnedel-Crafts alkylations (equation 12) that all proceed via carbamomc intermediates [729 7 7]... 

Taking into account the close relationship to pyridines one would expect 2-pyridones to express similar type of reactivities, but in fact they are quite different. 2-Pyridones are much less basic than pyridines (pKa 0.8 and 5.2, respectively) and have more in common with electron-rich aromatics. They undergo halogenations (a. Scheme 10) [67] and other electrophilic reactions like Vilsmeier formylation (b. Scheme 10) [68,69] and Mannich reactions quite easily [70,71], with the 3 and 5 positions being favored. N-unsubstituted 2-pyridones are acidic and can be deprotonated (pJCa 11) and alkylated at nitrogen as well as oxygen, depending on the electrophile and the reaction conditions [24-26], and they have also been shown to react in Mitsonobu reactions (c. Scheme 10) [27]. 

Ferrocene behaves in many respects like an aromatic electron-rich organic compound which is activated toward electrophilic reactions.In Friedel-Crafts type acylation of aromatic compounds with acyl halides, ferrocene is lO times more reactive than benzene and gives yields over 80%. However, ferrocene is different from benzene in respect to reactivity and yields in the Friedel-Crafts alkylation with alkyl halides or olefins. The yields of ferrocene alkylation are often very low. and the separations of the polysubstituted byproducts are tedious. 

The previous sections dealt with reactions in which the new carbon-carbon bond is formed by addition of the nucleophile to a carbonyl group. Another important method for alkylation of carbon nucleophiles involves addition to an electrophilic multiple bond. The electrophilic reaction partner is typically an a,(3-unsaturated ketone, aldehyde, or ester, but other electron-withdrawing substituents such as nitro, cyano, or sulfonyl also activate carbon-carbon double and triple bonds to nucleophilic attack. The reaction is called conjugate addition or the Michael reaction. 

Figure 1.11 Tyrosine residues are subject to nucleophilic and electrophilic reactions. The unprotonated phe-nolate ion may be alkylated or acylated using a variety of bioconjugate reagents. Its aromatic ring also may undergo electrophilic addition using diazonium chemistry or Mannich condensation, or be halogenated with radioactive isotopes such as 12iI.

The ring nitrogens react with electrophiles to afford either 1,3,4-thiadiazolium salts or l,3,4-thiadiazol-2(37/)-ones depending on the tautomerisability of the substituents at the C-2 or C-5 positions. While N-alkylation is the most common electrophilic reaction of 1,3,4-thiadiazoles, reactions with acyl and cyanogen halides as well as Mannich salts have also been reported. 

A review on the alkylation and related electrophilic reactions at endocyclic nitrogen atoms in the chemistry of tetrazoles has been published <00H(53)1421>. 

As the last point in Sect. IV, we discuss briefly the reactions of chiral sulfur compounds with electrophilic reagents. In contrast to nucleophilic substitution reactions, the number of known electrophilic reactions at sulfur is very small and practically limited to chiral tricoordinate sulfur compounds that on reacting with electrophilic reagents produce more stable tetracoordinate derivatives. It is generally assumed that the electrophilic attack is directed on the lone electron pair on sulfur and that the reaction is accompanied by retention of configuration. As typical examples of electrophilic reactions at tricoordinate sulfur, we mention oxidation, imination, alkylation, and halogenation. All these reactions were touched on in the section dealing with the synthesis of chiral tetracoordinate sulfur compounds. 

Mixed coupling between naphthalene and alkyl benzenes has also been demonstrated (Table 10, numbers 10-13). The relative yield of mixed coupling products increases with the basicity of the alkyl benzene with mesitylene 19%, with tetramethylbenzene 42%, and with pen-tamethylbenzene 64%. This suggests an electrophilic reaction between naphthalene cation radicals and alkylbenzenes. The mixed coupling reaction of phenan-threne with anisole has been studied kinetically [163]. 

The reaction of dialkylditellurides with pressurized acetylenes in the presence of an electrophilic reagent (alkyl halide, Lewis acid), in the system KOH/crown ether/ben-zene, gives rise to alkylethynyl tellurides and 1,2-bis-alkyltelluroacetylenes in high yields. ... 

In this review, we will initially describe the role of Bi(III) salts as activators for a-donors. In particular, benzyl and propargyl alcohols will be presented as mild electrophiles in alkylation reactions. In addition, we will show the versatility of Bi(III) salts and give a short overview of Bi(III)-catalyzed hydroarylation and hydroalkynylation reactions [23]. Besides our own results, which primarily focus... 

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