Arenes nucleophilic attack

Activation towards nucleophilic attack by withdrawing the e density from the arene by CpFe ... 

We examined the possibility of a direct formation of two C-C bonds by reaction of a carbanion with [Fe(arene)2]2+ in which the arene bears methyl groups. We could indeed repeat Hellings s experiments but found that mesitylene was the only aromatic allowing this possibility in reasonable yields. With p-xylene, a low yield of an unstable complex was obtained corresponding to double nucleophilic attack of phenyllithium on the same ring in spite of the bulk of the methyl groups [23]. Eq. (4) ... 

Fe+ + has been deprotonated, but the reaction is complicated by further nucleophilic attack of the methylene unit with the starting material [17]. Enhanced acidity of the ring hydrogens in arene-metal complexes is shown [21] by the formation of complexes of alkyllithium by proton abstraction. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Although deprotonation at the benzylic position of arenes coordinated to ruthenium and chromium was reported,27 in the case of the coordinated oxo-ri5-dienyl unit, nucleophilic attack at one terminus of the complexed r 5-dienyl ligand, rather than deprotonation, was expected.28 The reason for the successful deprotonation (even at relatively hindered isopropyl sites) is, according to the authors, the cationic nature of the Cp M fragment. In addition, the transition state for the deprotonation might involve stabilization by the metal (Scheme 3.15). 

Nucleophilic attack with electron-rich arenes and ethylene derivatives at C-7 of 5-methoxyfuroxano[3,4-d -pyrimidine 245 leads to 7-substituted 6,7-dihydro-5-methoxyfuroxano[3,4-r/]pyrimidines 246 (Equation 47) <2003JP0431>. 

Alkenes may be oxidized to epoxides that are reactive metabolites because of ring strain [36] and can undergo nucleophilic attack. Epoxides are not always highly reactive species. In fact, some of them are relatively unreactive for example, the arene oxides that derive from oxidation of phenyl rings. Most drugs containing a phenyl... 

The overall reaction catalyzed by epoxide hydrolases is the addition of a H20 molecule to an epoxide. Alkene oxides, thus, yield diols (Fig. 10.5), whereas arene oxides yield dihydrodiols (cf. Fig. 10.8). In earlier studies, it had been postulated that epoxide hydrolases act by enhancing the nucleo-philicity of a H20 molecule and directing it to attack an epoxide, as pictured in Fig. 10.5, a [59] [60], Further evidence such as the lack of incorporation of 180 from H2180 into the substrate, the isolation of an ester intermediate, and the effects of group-selective reagents and carefully designed inhibitors led to a more-elaborate model [59][61 - 67]. As pictured in Fig. 10.5,b, nucleophilic attack of the substrate is mediated by a carboxylate group in the catalytic site to form an ester intermediate. In a second step, an activated H20... 

Considerable advances were made in the organic chemistry of the methinyltricobalt enneacarbonyls. It was shown that the C03C core can function as an electron donor as well as an electron acceptor 143), allowing electrophilic and nucleophilic attack at the apical carbon atom. Arenes and Co3(CO)9CHal form Co3(CO)9CAr... 

An important feature of K-region arene oxides, which is not shared by the unsubstituted non-K-region oxides, is their susceptibility to nucleophilic attack and production of dihydrodiols. When there are electron-withdrawing substituents on the non-K-region arene oxides, their behavior is also similar to that of the K-region arene oxides. Later work has shown that in the study of 1 reported above, the chloride ions used in the medium were taking part, and... 

Very recently, the reaction of styrene 3,4-epoxide (245) with ethyl mercaptan has been reported.148 A mixture of 2-, 3-, and 4-ethylthiostyrenes is formed in the ratio of 1 9 7 along with small amounts (18%) of 4-vinylphenol. These results can be explained as nucleophilic attack on the intact arene oxide and the reaction of the zwitterion formed by the spontaneous reaction. 

A regioselective and highly syn-stereoselective catalyst-free intermolecular alkylation of aryl borates with aryl epoxides under mild, neutral conditions has been reported.27 The reaction of /ra .s-stilbene oxide with tri(3,5-dimethylphenyl)borate gave a 38% yield (>95% syn) of the C-alkylated product (13), easily separated from (g) the O-alkylated product(s). Triflic anhydride has been used to activate enones to nucleophilic attack by electron-rich arenes in the presence of a sterically hindered base.28 Resorcinol dimethyl ether, for example, reacted with cyclohex-2-en-l-one to... 

Arenes are inert to nucleophilic attack and normally undergo electrophilic substitution. However, arenes coordinate to Cr(CO)6 to form the i/fi-arenechromium tricarbonyl complex 79, and facile nucleophilic attack on the arene generates the anionic jy5-cyclohexadienyl complex 80, from which substituted arene 81, or cyclohexadiene is obtained by oxidative decomplexation. In this reaction, strongly... 

Arenes usually undergo electrophilic substitution, and are inert to nucleophilic attack. However, nucleophile attack on arenes occurs by complex formation. Fast nucleophilic substitution with carbanions with pKa values >22 has been extensively studied [44]. The nucleophiles attack the coordinated benzene ring from the exo side, and the intermediate i/2-cvclohexadienyl anion complex 171 is generated. Three further transformations of this intermediate are possible. When Cr(0) is oxidized with iodine, decomplexation of 171 and elimination of hydride occur to give the substituted benzene 172. Protonation with strong acids, such as trifluoroacetic acid, followed by oxidation of Cr(0) gives rise to the substituted 1,3-cyclohexadiene 173. The 5,6-trans-disubstituted 1,3-cyclohexadiene 174 is formed by the reaction of an electrophile. 

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