Phenols synthesis from aryl halides

Pd nanoparticles supported on PANI-NFs are efficient semi-heterogeneous catalysts for Suzuki coupling between aryl chlorides and phenylboronic acid, the homocoupling of deactivated aryl chlorides, and for phenol formation from aryl halides and potassium hydroxide in water and air [493], PANl-NF-supported FeCl3 as an efficient and reusable heterogeneous catalyst for the acylation of alcohols and amines with acetic acid has been presented [494]. Vanadate-doped PANI-NFs and PANI-NTs have proven to be excellent catalysts for selective oxidation of arylalkylsulfides to sulfoxides under nuld conditions [412]. Heterogeneous Mo catalysts for the efficient epoxidation of olefins with ferf-butylhydroperoxide were successfully synthesized using sea urchin-Uke PANI hollow microspheres, constructed with oriented PANI-NF arrays, as support [495]. Pt- and Ru-based electrocatalyst PANI-NFs—PSSA—Ru—Pt, synthesized by the electrodeposition of Pt and Ru particles into the nanofibrous network of PANI-PSSA, exhibited an excellent electrocatalytic performance for methanol oxidation [496]. A Pt electrode modified by PANI-NFs made the electrocatalytic oxidation reaction of methanol more complete [497]. Synthesis of a nanoelectrocatalyst based on PANI-NF-supported... 

The aryl r-butyl ether 15 and silyl ether 18, prepared by the Pd-catalyzed reaction, can be converted easily to phenols 16, and these reactions offer convenient synthetic methods for phenols 16 from aryl halides 14 and 17. Based on this reaction, the first synthesis of 4-chlorobenzofiiran (18c), which is difficult to synthesize by conventional methods, was carried out. Selective mono-r-butoxylation of 2,6-dichloroacetaldehyde dimethylacetal (18a) using P(r-Bu)3 as a ligand gave the r-butyl ether 18b, and subsequent treatment with aq. HCl afforded 4-chlorobenzofuran (18c) in 51 % overall yield. Further conversion of 18c to various 4-substituted benzofurans is possible by Pd-catalyzed substitutions of the 4-chloro group in 18c [6]. 

Apart from aryl halides, other very easily available substrates for nickel-catalysed biaryl (II) synthesis are aryl sulfonates (XII). Method D is very efficient in the homocoupling reactions of substituted aryl sulfonates in good to excellent yields [15], Table 6. Substituted aryl sulfonates are readily obtained from phenols and trifluoromethanesulfonic anhydride, benzenesulfonyl-, tosyl- or methanesulfonyl chloride in pyridine, or in a suitable inert solvent such as dichloromethane in the presence of triethylamine or Hiinig s base. Among other nickel complexes, Ni(dppe)Cl2 and Ni(dppf)Cl2 have been used (10 mo1%) as slightly less versatile catalysts for the homo-couplings of naphthyl sulfonates in refluxing THF, DMF or their mixtures [42]. 

Meyers and colleagues described the palladium-catalyzed carbonylative synthesis of oxazolines as early as 1992 [268]. Aryl or enol triflates made from the corresponding ketones and phenols, and also aryl halides, were used as starting materials and coupled with amino alcohols to give chiral a,)S-unsaturated or aryl oxazolines in good yields. Later on, Perry s group performed systematic studies on this one-pot, two-step process for the preparation of oxazolines (Scheme 2.37) [269, 270]. 

Arenethiols are important intermediates in chemical synthesis. While there are numerous reactions to introduce this functionality starting from aryl halides or phenols, most of these transformations require drastic reaction conditions and tolerate few if any functionalities. Despite the fact that in the last few years the efficiency of palladium-catalyzed cross-coupling reactions for the preparation of aryl ethers and aniline derivatives has improved greatly (see 5.1 and 5.2), analogous methods for the formation of aryl sulfides and especially arenethiols have lagged behind. The first report of a mild palladium-catalyzed synthesis of arenethiols came from Rane et followed by reports from a Zeneca Pharma group and a Merck group (Scheme 5-160). ... 

Xu, W. Mohan, R. Morrissey, M. M. Polymer-Supported Bases in Combinatorial Chemistry Synthesis of Aryl Ethers from Phenols and Alkyl Halides and Aryl Halides, Tetrahedron Lett. 1997, 38, 7337. 

Xu W, Mohan R, Morrissey MM, Polymer supported bases in combinatorial chemistry synthesis of aryl ethers from phenols and alkyl halides and aryl halides, Tetrahedron Lett., 38 7337-7340, 1997. 

The reactions between i-dinitrobenzene or 1,3,5-trinitrobenzene, aryl halides, and copper(I) oxide in quinoline 17-19, 21) provide a simple synthesis of nitrobiphenyls uncontaminated by symmetrical biphenyls. These couplings may be related to the Ullmann reaction, the decarboxylative coupling of benzoic acids with aryl halides, and the preparation of ethers from phenols 165). Although no intermediates... 

Koenigs-Knorr glycosidation Synthesis of alkyl or aryl O-glycosides from glycosyl halides and alcohols or phenols, respectively. 246... 

Diaryl ethers. This electron-rich and bulky / iV-ligand (1) facilitates the Pd-catalyzed synthesis of diaryl ethers from phenols and aryl halides. 

In an interesting paper, Xu et al. [19] have reported the combinatorial synthesis of aryl ethers 20 from phenols 16 and alkyl or aryl halides 18 by using PTBD (Scheme 5) ... 

The general synthesis of aryl xanthates is described by Schussler et al. 12). It follows from the ability of thallium(I) xanthates to undergo metathetical reactions with metal halides in absolute ethanol (Reaction 4). The thallium(I) precursors could be obtained with phenol... 

As noted in the introduction to this section, UUmann also reported the formation of biaryl ethers from phenol and phenyl bromide in the presence of copper and a base. This UUmann ether synthesis has been used extensively to prepare biaryl ethers. " However, the original reaction conditions involved high temperatures (150-200 C), neat phenol or highly polar aprotic solvents, and stoichiometric amounts of copper complexes. The yields for the reactions of unactivated aryl halides were often low. Conditions with catalytic amounts of copper at lower temperatures with broader scope have now been developed. 

The most common preparative method to prepare the aryl allyl ether is the Williamson s ether synthesis [la,b]. Typically, aryl allyl ethers can be obtained from phenol derivatives and allylic halide under basic conditions (KjCOj) in refluxing acetone. This method is convenient for the preparation of simple allyl aryl ethers. However, some side reactions such as a competitive C-allylation (Sn2 type reaction) often accompany the formation of undesired byproducts. Mitsunobu reaction of phenol derivatives with allylic alcohols instead of allylic halides can be used under mild conditions [13]. In particular, when the allyl halide is unstable, this procedure is effective instead of the Williamson s ether synthesis. This method is also useful for the preparation of chiral allyl aryl ether from chiral allylic alcohol with inversion at the chiral center. Palladium catalyzed O-allylation of phenols is also applicable, but sometimes a lack of site-selectivity with unsymmetrical allylic carbonate [14] may be a problematic issue. 

An apparent exception to the generalization about the lack of reactivity of aryl halides to nucleophilic substitution is an early industrial process for the synthesis of phenol from chlorobenzene. When heated at 300°C under high pressure with aqueous NaOH, chlorobenzene is converted to sodium phenoxide. Neutralization of this salt with aqueous acid gives phenol. 

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