Anions Anisole

In a recent publication, D. A. Burnham [Tetrahedron, 25, 897 (1969)] presents other calculations which indicate that protonation of the radical-anion of anisole is more likely to occur meta to the methoxyl group rather than ortho as Zimmerman proposes. 

Trifluoroacetic acid removes tert-butyl-based protectors by the S vl mechanism, with the cation being trapped by the trifluoroacetate anion however, the tert-butyl trifluoroacetate produced is an alkylating agent, and the acid is not strong enough to protonate the side chains of methionine, tryptophan, and cysteine, so these are acceptors of tert-butyl. A scavenger is required to prevent their alkylation. Anisole... 

Anionic rhodium complexes, 32 356-364 Anionic ruthenium complexes, 32 402-406 Anions, 32 224 Anisole... 

Let ns direct onr attention to the difference between the anion-radicals 804 and COj". While the latter is a one-electron rednctant (see section 1.7.4), the former is a one-electron oxidant. One-electron transfer from a snbstrate to the snlfate radical mostly follows diffusion rates. For instance, rate constants of one-electron oxidation of benzene and anisole with SO4 are equal to 3 X 10 and 5 X 10 L mol s respectively (Goldstein and McNelis 1984). 

The reaction in Scheme 5.11 gives the snlfoninm salt (anion CIO4 ) in a 90% yield (ronte a). One-electron reduction of the thianthrene cation-radical by anisole is the side reaction (ronte b). Route b leads to products with a 10% total yield. Addition of the dibenzodioxine cation-radical accelerates the reaction 200 times. The cation-radicals of thianthrene and dibenzodioxine are stable. Having been prepared separately, they are introdnced into the reaction as perchlorate salts. 

It was realized that the mechanism of Birch reduction involves protonation of the anion-radical formed by the addition of one electron to the reacting aromatic compound. This is followed by rapid addition of a second electron and protonation of the forming carbanion to yield nonconjugated alicyclic products. Protonation of the anion-radical by added alcohol is the rate-limiting stage. Recent calculations show that the ortho and meta positions in anisole are most enhanced in density by electron introduction. The para position is not appreciably affected (Zimmerman and Alabugin 2001 Scheme 7.9). 

Another experiment in which sequential adsorption of phenol and pyridine then followed by methanol shows formation of pyridinium ion and phenolate anion whereas no traces of methanol or electrophilic methyl species or formation of methylated products were identified on the catalysts surface. This result was supposedly confirmed from another experiment in which anisole and methanol were co-adsorbed on the catalyst. The spectra were referred to the molecular species of methanol and anisole without any significant interaction among them and above 200°C they simply desorbed from the catalyst. 

Figure 1 contains chromatograms of polystyrenes prepared anionically in the presence of anisole and diphenyl ether. The narrow molecular weight distributions of these samples demonstrate that no detectable termination took place during the polymerizations. This lack of a termination step, regarding anisole, is in agreement with the polymerization results (34,35,36,37) where this ether was used as a co-solvent. 

Syndiotactic polypropylene has been made by Zambelli, Natta and Pasquon (75). The anionic catalysts made from dialkylaluminum chloride, vanadium acetylacetonate and anisole reverse the addition to the propylene molecule so that control by an ultimate asymmetric carbon is no longer possible. The formation of syndiotactic polypropylene is shown in Fig. 8 close to the region of inverted reaction of the propylene molecule. 

The reaction of p-iodo- or p-bromo-anisole or of 1-iodonaphthalene with the anion formed from the a,(3-unsaturated nitrile (36) gives 60-70% combined yields of the isomeric nitriles (37) and (38) together with small amounts of the diarylated derivatives (39).135... 

The meta acylation of anisole, using a carbonyl anion equivalent as the nucleophile, illustrates the unique regioselectivity available with the Cr(CO)3 activation (equation 31). 

Remarkably few systematic studies have been made of the kinetics of anionic polymerization in non-polar solvents containing small amounts of ethers in contrast, studies of bulk ether systems abound. Several studies have appeared 156 158) in which the propagation reactions involving styryllithium were measured in mixtures of benzene or toluene with ethers. The kinetic orders, in some cases, of the reactions were identical to those observed in the absence of the ether. Thus, in part, the conclusion was reached 157,1581 that the ethers did not disrupt the dimeric degree of aggregation of poly(styryl)lithium. The ethers used were tetrahydrofuran 156), anisole 157), diphenyl ether 158), and the ortho and para isomers of ethylanisole157). 

A number of papers report investigations of the pyrolytic cleavage of aromatic hydrocarbons. The oxidation and pyrolysis of anisole at 1000 K have revealed first-order decay in oxygen exclusively via homolysis of the O—CH3 bond to afford phenol, cresols, methylcyclopentadiene, and CO as the major products.256 A study of PAH radical anion salts revealed that CH4 and H2 are evolved from carbene formation and anionic polymerization of the radical species, respectively.257 Pyrolysis of allylpropar-gyltosylamine was studied at temperatures of 460-500 °C and pressures of 10-16 Torr. The product mixture was dominated by hydrocarbon fragments but also contained SO2 from a proposed thermolysis of an intermediate aldimine by radical processes.258... 

The available rate data for the substitution reactions of phenol, diphenyl ether, and anisole are summarized in Table 5. The elucidation of the reactivity of phenol is hindered by its partial conversion in basic media into the more reactive phenoxide anion. Because of the high reaction velocity of phenol and the even greater reactivity of phenoxide ion the relative rates are difficult to evaluate. Study of the bromination of substituted phenols (Bell and Spencer, 1959 Bell and Rawlinson, 1961) by electrochemical techniques suitable for fast reactions indicates the significance of both reaction paths even under acidic conditions. 

Ohashi et al. [136,139] have proposed a scheme describing the formation of ortho adducts and substitution products from anisole and the three dimethoxyben-zenes with acrylonitrile, methacrylonitrile, and crotonitrile (Scheme 39). Here, the ortho cycloadduct is supposed to be formed directly from an encounter complex or exciplex, whereas the substitution product arises via formation of an ion pair from the complex, followed by protonation of the radical anion and radical... 

When the irradiation was performed in MeOD, incorporation of one deuterium atom into the a-methyl groups could be demonstrated. The reaction proceeds via photoinduced electron transfer from the excited anisole to acrylonitrile, possible in an exciplex [139], The radical anion of acrylonitrile abstracts a proton from the solvent and the resulting radical combines with the radical cation of anisole forming a a-complcx that finally loses a proton. 

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