Lewis basic phenol

Common organic functionality such as Lewis basic phenol 3, acid-labile acetal 4, highly reactive aryl friflate 6, and depsipeptide 5 are well-tolerated under the mild reaction conditions (Figure 2). In all cases the products are isolated as one regioisomer and olefin isomer after column purification. 

Treatment of commercially available and symmetrical 3,4,5-tri-methoxytoluene (37) with iodine, periodic acid, and acetic acid under the conditions of Suzuki19 results in the formation of symmetrical diiodide 38 in 93 % yield. Although only one of these newly introduced iodine atoms is present in intermediate 13, both play an important role in this synthesis. Selective monodemethylation of 38 with boron trichloride furnishes phenol 39 in 53% yield together with 13 % of a regioisomer. Evidently, one of the Lewis-basic iodine substituents coordinates with the Lewis-acidic boron trichloride and directs the cleavage of the adjacent methyl ether... 

The QSC value of the lithium phenolate tetramer in THF solution is between 40 and 46 kHz at —67 and +30 °C, respectively. For other tetramers the QSC ranges from 35 to 57 kHz, depending on substitution pattern and solvent. It was observed that the magnitude of the observed QSC values correlates with the Lewis basicity of the solvent. 

Those solutes for which the solvent shifts are particularly large have been used in the specification of solvent properties, such as electron-pair donation ability, Lewis basicity, or softness. For the former property, the solvent shifts of deuteromethanol or of phenol have served as suitable scales. For the latter property the solvent shifts of the symmetrical stretch of Hg-Br in the Raman spectrum of HgBr2 and of I-CN in the infrared spectrum of ICN have been so employed (see Chapter 4). 

In a similar way, another set of solvent Lewis-basicity parameters, i phOH) based on band shifts of the O—H stretching vibration of phenol in tetrachloromethane induced by hydrogen-bond formation with added HBA solvents B, was used by Koppel and Paju [88] to classify 198 solvents, according to Eq. (7-36) (5phOH = 0 for CCI4) ... 

We noted in Section 16-3 that electrophilic attack on benzenamine (aniline) and phenol are difficult to stop at the stage of monosubstitution because of the highly activating nature of the NH2 and OH groups. In addition, with these Lewis basic functions, complications can... 

The first set of equilibrium constants for the hydrogen bonding of a large number of diverse Lewis bases to a given hydrogen-bond donor, in the same conditions of temperature and solvent, which should permit the construction of a Lewis basicity scale, refers to phenol at 20 °C in CCI4. The association constants between phenol and about 200 Lewis bases... 

Demethylation of poly(sulfonium cation) occurs by nucleophile substitution reaction via Sn2 mechanism The demethylation is also classified as a transmethylation to nucleophiles. Using nucleophiles that have a mobile proton such as phenol, aniline and benzoic acid derivatives in the presence of potassium carbonate, demediyladon of poly( sulfonium cation) proceeds efficiently to yield the methylated products of phenol and benzoic acid with 100 % conversion (Scheme 2). In the case of aniline, both N-methyl and M -dimethyl aniline are obtained and methylation of -methyl aniline occurs more easily than aniline because of the higher Lewis basicity. 

Shibasaki has described the use of bifunctional catalysis in asymmetric Strecker reactions, using BlNOL-derived Lewis acid-Lewis base catalyst 160 (Equation 24) [114]. The aluminum complex had previously been shown to catalyze enantioselective cyanohydrin formation (Chapter 2, Section 2.9) [115]. In the proposed catalytic cycle, the imine is activated by the Lewis acidic aluminum while TMSCN undergoes activation by association of the silyl group with the Lewis basic phosphine oxide. Interestingly, the addition of phenol as a putative proton source was beneficial in facilitating catalyst turnover. The nature of the amine employed for the formation of the N-substituted aldimine proved to be vital for enantioselectivity, with optimal results obtained for N-fluorenyl imines such as 159, derived from aliphatic, unsaturated, and aromatic aldehydes (70-96% ee) [114],... 

Mg/Me (Me=Al, Fe) mixed oxides prepared from hydrotalcite precursors were compared in the gas-phase m-cresol methylation in order to find out a relationship between catalytic activity and physico-chemical properties. It was found that the regio-selectivity in the methylation is considerably affected by the surface acid-basic properties of the catalysts. The co-existence of Lewis acid sites and basic sites leads to an enhancement of the selectivity to the product of ortho-C-alkylation with respect to the sole presence of basic sites. This derives from the combination of two effects, (i) The H+-abstraction properties of the basic site lead to the generation of the phenolate anion, (ii) The coordinative properties of Lewis acid sites, through their interaction with the aromatic ring, make the mesomeric effect less efficient, with predominance of the inductive effect of the -O species in directing the regio-selectivity of the C-methylation into the ortho position. 

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