Phenols polysubstituted

The arylation of electron-rich arenes, such as azulene (55)206 and heteroarenes, has been sporadically described. Under similar conditions phenols undergo arylation, which is preferably directed at the ort/zo-positions, probably due to the involvement of palladium phenolate intermediates.188,207 Polysubstitution occurs readily.208 The para-position can be attacked only with the sterically hindered 2,6-di-t-butylphenol.209 Similar ortho-diarylation of arenes bearing carbonyl groups (acetophenone, anthrone, benzanilide, etc.) shows that the or//zo-di reeling effect of the substituent is more important than its other electronic effects.189... 

The synthesis of 3-aryltetrahydroisoquinolines was accomplished by electrophilic aromatic substitution of polysubstituted phenols and phenyl ethers with Lewis acid-generated tosyliminium ions of 2-tosyl-3-methoxytetrahydroisoquinoline derivatives <00SL801>. In addition isoquinoline was reported to react with N-tosylated (R)- or (S)-amino acid fluorides to afford optically active dihydroimidazoisoquinolinones. The reaction proceeds via acylation followed by attack of the tosylamino group at Cl of the intermediate 2-tosylaminoacylisoquinolinium salt <00TL5479>. 

Because of the differential partitioning of hydroxide and phenoxide anions into organic solvents by quaternary ammonium cations, the catalysts generally have little effect on the Reimer-Tiemann reaction of phenols with dihalocarbenes [15]. Cetyltrimethylammonium bromide has been used in the two-phase dichloromethyl-ation of polysubstituted phenols (Scheme 7.21, Table 7.10) under Makosza s conditions [16,17] ring expansion of the reaction products provides an effective route to tropones. The rate of the reaction is enhanced by ultrasonic radiation [16]. 

Special mild conditions are needed to achieve electrophilic monosubstitution in phenols because their high reactivity favors both polysubstitution and oxidation. 

In order to determine the applicability of the additivity principle for polysubstituted models, the rate data in Table III have been expressed in terms of partial rate factors of individual substituent groups in Table IV. The partial rate factors for polysubstituted compounds are calculated on the same basis as those of monosubstituted ones. For instance, the partial rate factors in guaiacol refer to the factors by which the rate constants of phenol are modified in positions 3, 4, 5, and 6 by introducing a methoxyl group in position 2. Likewise, the partial rate factors for methoxyl in 4-hydroxy-3,5-dimethoxytoluene indicate how the protodedeuteration rates of 4-hydroxy-3-methoxytoluene at positions 2 and 6 are modified by inserting a methoxyl group at position 5. 

Also, the [4+2] benzannulation of enyne 154 with diyne 155 proceeds chemo- and regioselectively to afford 156 [66], A similar reaction of enyne silyl enol ether 157 with the diyne offers a good synthetic route to polysubstituted phenols 159 via 158 [67]. In this reaction enol silyl ethers having the (E) configuration as shown in 157 give satisfactory results. 

Regioselectivity of the Birch reductive alkylation of polysubstituted biaryls is affected by the electronic nature of substituents on both aromatic rings. The electron-rich 3,5-dimethoxyphenyl moiety is selectively reduced and then alkylated, whereas phenols and aniline are not dearomatized under these conditions. Biaryls possessing a phenol moiety are alkylated on the second ring, provided that the acidic proton has been removed prior to the Li-NH3 reduction.300... 

Two approximations usually applied in plotting Hammett relations for phenols are the assumed equality of ortho and para positions and an expected additivity of single substituent effects for polysubstituted cases. It is clear that neither of these can be exactly valid, although recent evidence shows that both approximations are fairly good for the acidity of phenols (Bolton et al., 1970 Sucha et al., 1970). 

Nitration takes place easily and again there is a tendency for polysubstitution. Phenols are readily nitrosated by nitrous acid. The resultant nitrosophenols are tautomeric with the corresponding quinone monoximes (Scheme 4.16). 

The first completely synthetic ion exchange resins were prepared by B. A. Adams and E. L. Holmes in 1935. The basis of their synthesis was the condensation polymerization of methanal (formaldehyde) with phenol or polysubstituted benzene compounds to give, after... 

With phenols, as with amines, special precautions must often be taken Ao prevent polysubstitution and oxidation. - ... 

Modifications of these resins are also known. For example, aluminum phenoxide bonded to an acidic E)owex resin has been used as a heterogeneous catalyst for alkylation and transalkylation of phenols and polysubstituted phenols, respectively. ... 

An intramolecular Michael reaction (catalyzed by 2C) following the oxidative dearomatization of 4-substituted phenols provides valuable octalones. A method involving two consecutive Michael reactions to form optically active polysubstituted cyclopentanes should be highly rated. 

In the place of Cl and Br in the above examples any univalent atom or radical may be substituted, thus giving rise to a gx t number of deriva-tivea Certain of such substituted radicals determine the function of the original unisubstituted derivative of benzene and of all of its polysubstituted derivatives Thus the group (OH) is characteristic of the phenols (CH,) or + of the superior homologues of benzene (CH,OH) of the... 

Several different organometallic reagents have been used for the synthesis of polysubstituted phenols. Thus the vinylcyclopropene depicted, underwent carbonylation and rearrangement in benzene solution, containing a little tetracarbonyidichlorodirhodium, with carbon monoxide at 80°C under 1 atmosphere pressure to afford 5,6-diethyl-3-phenyl-2-propylphenol in 82% yield (ref. 15). 

Organic aerosols formed by gas-phase photochemical reactions of hydrocarbons, ozone, and nitrogen oxides have been identified in both urban and rural atmospheres (Grosjean, 1977). Most of these species are di- or poly-functionally substituted alkane derivatives. These compounds include aliphatic organic nitrates (Grosjean and Friendlander, 1975), di-carboxylic acids (adipic and glutaric acids) (O Brien et al., 1975), carboxylic acids derived from aromatic hydrocarbons (benzoic and phenylacetic acids), polysubstituted phenols, and nitroaromatics from aromatic hydrocarbons (Kawamuraet al., 1985 Satsumakayashi et al., 1989, 1990). Some species that have been identified in ambient aerosol and are be-... 

Certain compounds (electrophilic) can react with phenols (nucleophilic). The nucleophilic activity can be either in the iaromatic ring or the oxygen in the hydroxyl group. Examples of electrophilic aromatic substitution include nitration, halogenation, Friedel-Crafts reactions (alkylation and acylation), and sulfonation. The halogenation example shown below is a polysubstitution reaction involving bromine. The polysubstitution usually occurs when polar solvents are used. 

Rigby s studies on the synthesis of alkenylisocyanates fostered the preparation of a suitable substituted aryl enamide, which on photocyclization yielded the polysubstituted pentacyclic system. Key to the success of this process is the hydrogen bond between the phenolic OH and the carbonyl group, which restricts the rotation around the aryl-amide bond and directs the cyclization. Further functionalization allowed the total synthesis of pancratistatin (272) and narciclasine (68) (275) (Scheme 11). The [4-1-1] cycloaddition of bis(alkylthio)carbenes with vinyl isocyanates was the key process in a recent synthesis of (+)-mesembrine (92) 274). 

Compounds 115 with an ester group at have been subjected to aldol-type or Dieckmann cyclization by treatment with t-BuOK in THF to give six-membered ring intermediates 116 in 63-71% yields the use of DBU as base did not give the desired product 116 (Scheme 4.33). Aromatization could then be achieved to furnish polysubstituted phenol derivatives 117 in 44-76% yields in the presence of DBU. However, the reactant 115 containing a cyano group at... 

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