C-Alkylations of phenolates

Zeolites H-BEA and H-Y were found to be the most active catalysts, however all catalysts readily form the phenyl benzoate (Table 4.1). In the conditions of the reaction, the formation of phenyl benzoate (PB) occurs rapidly via O-acylation of phenol. Direct C-alkylation of phenol with benzoic anhydride (B) and Fries rearrangement of phenyl benzoate results in the formation of 2- and 4-hydroxy-benzophenones (2-HPB and 4-HPB) (Scheme 4.3). 

The first molecules retained in the zeolite are polymethylphenols or anisoles formed through several 0 and C alkylations of phenol. Thus the formation of the main components in the A family requires 6 steps catalyzed by acid sites. 

Activation of the C-0 bond in the allylic carbonates promoted by a palladium complex with a chiral ligand as shown in Eq. 17 leads to asymmetric 0- and C-alkylation of phenols [39]. 

Lewis acids immobilized on ionic liquids have been used as the acid catalysts for the alkylation of phenols. The catalytic activities of the immobilized ionic liquids were found to be higher than those for the zeolites. Typically, ionic liquids such as butylmethyUmi-dazoUum halides are treated with AICI3 to give the ionic liquids with halogenoaluminates as the counter anions. They show enhanced Lewis acid character and promote predominantly C-alkylation of phenols over O-alkylation. The alkylation of phenol with dodecene, for example, in the presence of these immobilized ionic liquids results in up to 70% of C-alkylated products (ortho and para products) and 30% of O-alkylated product, comparable to zeolite catalysis (equation 23). The rates of alkylation of phenols are slower than those of arenes due to the complexation of the phenolic group with the Lewis acidic ionic liquids. At higher temperatures conversions of up to 99% could be achieved. 

Thermal C-alkylation of phenols with ethylene derivs. 

O- and C-Alkylation of phenols s. 14, 284 Acoxy compounds from bromides Br OAc... 

Magnesium iodide s. under Mg Zinc chloride C-Alkylation of phenols s.ll, 894... 

Boron fluoride (s. a. under HJPO4) C-Alkylation of phenols with ethylene derivatives... 

The scope of this F-C hydroxyalkylation of indoles was extended to a range of different carbonyl compounds, giving rise to the desired compounds in high yields (up to 97%) and enantioselechvities (up to 99% ee) in the presence of catalysts 13 and 14 [18]. Catalyst 14 also proved to be highly selective when carrying out the first example of cinchona alkaloid mediated F-C alkylation of phenols with 45 (Scheme 35.8) [58]. Chiral phosphoric acids were also used to mediate F-C alkylation in the presence of ethyl trifluoropyravate [31], trifluoroacetate [59], and trif-luoromethyl ketones [60]. 

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