Methoxybenzene, alkylation

The Y appendage of 2-cyclohexenone 191 cannot be directly disconnected by an alkylation transform. (y-Extended enolates derived from 2-cyclohexenones undergo alkylation a- rather than y- to the carbonyl group). However, 191 can be converted to 192 by application of the retro-Michael transform. The synthesis of 192 from methoxybenzene by way of the Birch reduction product 193 is straightforward. Another synthesis of 191 (free acid) is outlined in... 

For the Birch reduction of mono-substituted aromatic substrates the substituents generally influence the course of the reduction process. Electron-donating substituents (e.g. alkyl or alkoxyl groups) lead to products with the substituent located at a double bond carbon center. The reduction of methoxybenzene (anisole) 7 yields 1-methoxycyclohexa-1,4-diene 8 ... 

In 1999, Ikeda et al. reported a new type of sulfur-oxazoline ligands with an axis-fixed or -unfixed biphenyl backbone prepared in good yields by coupling reactions of methoxybenzene derivatives substituted with a chiral oxazoline and a sulfur-containing Grignard reagent. These ligands were subsequently evaluated for the test palladium-catalysed asymmetric allylic alkylation... 

The structure of the products is determined by the site of protonation of the radical anion intermediate formed after the first electron transfer step. In general, ERG substituents favor protonation at the ortho position, whereas EWGs favor protonation at the para position.215 Addition of a second electron gives a pentadienyl anion, which is protonated at the center carbon. As a result, 2,5-dihydro products are formed with alkyl or alkoxy substituents and 1,4-products are formed from EWG substituents. The preference for protonation of the central carbon of the pentadienyl anion is believed to be the result of the greater 1,2 and 4,5 bond order and a higher concentration of negative charge at C(3).216 The reduction of methoxybenzenes is of importance in the synthesis of cyclohexenones via hydrolysis of the intermediate enol ethers. 

Menon presented a set of interesting liquid crystals 48 (Scheme 25) based on dibenzo[18]crown-6 modified with 2-hydroxy-3-methoxybenzene (48a), 3,4,5-trimethoxybenzene (48b), thiophene (48c), and pyrrole (48d) linked via a Schiff base [63]. All compounds are lacking long alkyl chains in the periphery. Nonetheless, broad mesophases with different geometries (SmC, SmA, N) were observed. 

When the sodium salt of a phenol is treated with an alkyl halide or an alkyl sulfate, 0-alkylation occurs and an ether is formed, usually in good yield. Methyl ethers such as anisole (methoxybenzene) can also be formed in excellent yield by treatment of a phenol with diazomethane (Scheme 4.8). 

The reaction of vinyldiazocarbene 17 parallels that observed with methoxybenzenes. Due to the ability of the nitrogen to stabilize a positive charge, only the alkylation product 168 is obtained. Methyl pyrrole-l-carboxylate, however, on reaction with 17 affords the tropane skeleton... 

Another alternative approach primarily intended for the synthesis of 3-alkylphenols consisted in the reaction of (i) alkylmagnesiumbromides with 3-methoxybenzamide to afford the corresponding 3-methoxyphenyl n-alkylketone which was reduced (ii) by the Clemmensen method to the n-alkyl-3-methoxybenzene, demethylation of which with aluminium chloride was considered to give the 3-n-alkylphenol (ref. 15). 

The zeolite-catalysed alkylation of phenol or anisole (methoxybenzene) with methanol is a complex sequence of reactions taking place within ZSM-5 and ZSM-11 at 200-300 °C. As shown in Figure 4.3 (overleaf), the primary products are anisole and cresols (ortho-, rneta- and /7ara-methylphenols), but lesser amounts of xylenols (dimethylphenols) and methylanisoles are also found. Alkylation of both the benzene ring and the oxygen atom is faster when zeolite Y is used, but the selectivity for ortho-crQsol is greater when ZSM-5 or ZSM-11 is the catalyst. 

In contrast to the reactions with benzene, the reactions of 4 with 1-methoxybenzene, 1,2-dimethoxybenzene, and 1,2,3-trimethoxy-benzene result in the formation of the alkylation products 65 in... 

Alkylhalide (RH) exists in the CA resist layer. An alkyl group is reacted with p-methoxybenzene to produce acid H+CF3S03 by UV light. Thus, acid H+ is produced from thianthrenium by UV irradiation. 

The fourth item in the table, phenol (hydroxybenzene), is alkylated on oxygen, forming an ether, methoxybenzene (anisol), with the powerful alkylating agent trimethyloxonium tetrafluoroborate [(CH30)3 BFt]. Other alkoxonium tetrafluo-roborates are also commercially available and can be used to the same end with phenols, enols, and alcohols, forming aryl ethers, enol ethers, and dialkyl ethers, respectively. In contrast to dialkyl, diaryl, and aralkyl ethers, which are quite inert and are often used as solvents, enol ethers are capable of acid-catalyzed hydrolysis to produce ketones (or their equivalent enol) and the alcohol from which the enol ether is formed (Scheme 8.47). 

Pan and Xue reported pillar[5]arene derivatives with three different kinds of repeating unit (Scheme 3.18). Per-allqrlated pillar[5]arenes are oxidized upon addition of oxidants, but per-methojq carbonyl-methojgr-substituted pillar[5]arene was not oxidized under the same oxidation conditions as the per-alkylated pillar[5]arenes. This indicates that l,4-metho3qrcarbonyl-methoxybenzene units exhibited oxidative resistance when compared with l,4-dialko)ybenzenes. Based on this finding. Pan and Xue first synthesized four methoxycarbonyl-methojqr-substituted pillar[5]arene (3.112) from Al/ A2/C1/C2 tetra-hydroxylated pillar[5]arene (3.108). Oxidation of 3.112 afforded pillar[5]arenes with one (3.113), two (3.114) and three benzoquinone moieties (3.115). Because the metho>ycarbonyl-metho3q -substituted units show oxidative resistance, the A and C units, which modified methojqr-carbonyl-methojy groups, were not oxidized. ... 

Foods may contain a number of alkyl aryl ethers that are components of essential oils of different spices as well as secondary substances. These ethers are most often derived from anisole (methoxybenzene, 8-33) or veratrole (1,2-dimethoxybenzene, 8-33), which are substituted by a prop-l-en-yl or l-prop-2-en-l-yl (allyl) group at the C-4 position of the benzene ring. An important ether is estragole (also known as 4-aUylanisole or methyl chavicol, 8-33), which is the main component (over 80%) of basil essential oil (see Table 8.32, later) and tarragon (dragon s wort) essential oil... 

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