Alkyl methyl carbonates, phenol

TABLE 4.8 Reactions of Phenol with Different Alkyl Methyl Carbonates"... 

Methyl ethers are usually prepared by some variant of the Williamson ether synthesis in which an alcohol reacts with either iodomethane, dimethyl sulfate, or methyl triflate (HAZARD) in the presence of a suitable base. A word of caution dimethyl sulfate and methyl triflate, tike all powerful alkylating agents, are potentially carcinogenic and therefore should only be handled in a well-ventilated fume hood. For the 0-methylation of phenols (pKa 10) a comparatively weak base such as potassium carbonate in conjunction with dimethyl sulfate is sufficient,193 whereas simple aliphatic alcohols require stronger bases such as sodium hydride [Scheme 4.111]22 or lithium hexamethyldisilazide [Scheme 4.112].203 The latter transformation is notable for the fact that 0-methyiation was accomplished without competing elimination. 

The palladium(0)-catalyzed asymmetric O-allylation of phenols has been described using five-, six- and seven-membered ring allylic carbonates and acyclic allylic carbonates (eq 9). The products from these reactions were subjected to a Claisen rearrangement to provide C-alkylated phenols. A study of various ligands for the reaction of phenol with 2-cyclohexenyl-l-methyl carbonate clearly showed that the Trost ligand is superior. ... 

The products of the asymmetric alkylation have been used as key building blocks in syntheses of morphanes, phyllanthocin, and periplanone B natural products. In the case of the synthesis of the morphane skeleton, a phenolic nucleophile was reacted with cyclohexenyl methyl carbonate and the resulting ether was subjected to a europium-induced Claisen rearrangement followed by an intramolecular aldehyde-ene reaction to generate the key tricyclic intermediate. Scheme 27 [56]. 

Methoxyarenes. Phenols undergo O-methylation with methyl carbonates (K2CO3-D. 1F, 150°). Comparing to dimethyl carbonate the unsymmetrical carbonates with the. then alkyl group larger than propyl can be used in an open flask. 

Deprotonation of phenol (P20.2) gives an anion which is equivalent to the enolate anion of cyclohexadienone (P20.3). This can be alkylated on carbon, rather than oxygen, if the reaction conditions are correct. The product ketone (P20.4) can be re-enolised to give o-cresol (P20.5) and the whole process repeated. After the addition of three methyl groups, the product ketone (P20.1) cannot enolise and so the alkylation process ceases (Figure S20). 

Alcohols are compounds that contain -OH groups connected to an alkyl carbon. Phenols are similar, but have an -OH group connected directly to an aromatic ring. The terms primary, secondary, and tertiary are used to describe aicohois. in a primary alcohol, a carbon can be connected to one or no other carbon atoms example CH3-OH, methyl alcohol. A secondary is connected to two carbons example isopropyl alcohol. Tertiary describes connections to three other carbons example tert-butyl alcohol (Figure 19-7). 

Synthesis of carbonates (Homogeneous catalyst) alkyl phenyl carbonate from dialkyl carbonate and phenol 2-hydroxyethyl methyl carbonate from dimethyl carbonate... 

Alkylphenols containing 3—12-carbon alkyl groups are produced from the corresponding alkenes under acid catalysis. Alkylphenols containing the methyl group were traditionally extracted from coal tar. Today they are produced by the alkylation of phenol with methanol. 

Carbon disulphide methanol phenol n-hexane methyl n-butyl ketone organophosphorus compounds tetra-alkyl lead compounds. 

For carbon-carbon bond-formation purposes, S 2 nucleophilic substitutions are frequently used. Simple S 2 nucleophilic substitution reactions are generally slower in aqueous conditions than in aprotic organic solvents. This has been attributed to the solvation of nucleophiles in water. As previously mentioned in Section 5.2, Breslow and co-workers have found that cosolvents such as ethanol increase the solubility of hydrophobic molecules in water and provide interesting results for nucleophilic substitutions (Scheme 6.1). In alkylations of phenoxide ions by benzylic chlorides, S/y2 substitutions can occur both at the phenoxide oxygen and at the ortho and para positions of the ring. In fact, carbon alkylation occurs in water but not in nonpolar organic solvents and it is observed only when the phenoxide has at least one methyl substituent ortho, meta, or para). The effects of phenol substituents and of cosolvents on the rates of the competing alkylation processes... 

We have concluded that in order to obtain the stable polysilane containing a phenol group our synthesis requires that a small alkyl group such as methyl must be a companion substituent on silicon, the phenolic group must be separated from Si by two carbons or more, and the position of the OH group on the aromatic ring must be preferably meta.(Figure 5). 

This includes bioremediation cases of contaminated sites with several toxic and carcinogenic pollutants, such as petroleum hydrocarbons, PAHs, dichlorobenzene, chlorinated hydrocarbons, carbon tetrachloride, Dicamba, methyl bromide, trinitrotoluene, silicon-based organic compounds, dioxins, alkyl-phenol polyethoxylates, nonylphenol ethoxylates, and polychlorinated biphenyls. The following is a brief summary of each case. 

Unsubstituted cycloamyloses have been used to catalyze a number of reactions in addition to acyl group transfer. Brass and Bender (8) showed that cycloamyloses promoted phenol release from diphenyl and bis(p-nitro-phenyl) carbonates and from diphenyl and bis(m-nitrophenyl)methyl phos-phonates. Breslow and Campbell (10,11) showed that the reaction of anisole with HOCL in aqueous solution is catalyzed by cyclohexaamylose and cycloheptaamylose. Anisole is bound by the cyclodextrins and is chlorinated exclusively in the para position while bound. Cycloheptaamylose has been used to promote regiospecific alkylation followed by the highly selective oxidation shown in reaction (3) (95). In addition cycloheptaamylose effec-... 

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