Aryl alkyl ethers oxidation

A recent publication has shown that aryl alkyl ethers can be formed through a G-H bond oxidative functionalization process in a regioselective manner when an adequate directing group is present (Equation (129)).401,495 Mechanistic studies have provided evidence for the involvement of a Pd(iv) intermediate.496... 

The reaction described is of considerable general utility for the preparation of benzoyloxy derivatives of unsaturated hydrocarbons.2"8 Reactions of 2-butyl perbenzoate with various other classes of compounds in the presence of catalytic amounts of copper ions produce benzoyloxy derivatives. Thus this reaction can also be used to effect one-step oxidation of saturated hydrocarbons,9, 10 esters,6,11 dialkyl and aryl alkyl ethers,12 14 benzylic ethers,11,15 cyclic ethers,13,16 straight-chain and benzylic sulfides,12, 17-19 cyclic sulfides,11,19 amides,11 and certain organo-silicon compounds.20... 

Ni(0) complexes react with halides and pseudohalides. Their reactions are somewhat different from those of Pd(0). Chlorides add to Ni(0) much more easily than to Pd(0). Even C—O bonds such as aryl alkyl ether bonds are cleaved with Ni(0) under certain conditions. Not only triflates, but also mesylates react with Ni(0). Oxidative addition to Ni(0) and subsequent transformations are summarized in Scheme 3.6. 

This oxygenation reaction proceeds under milder conditions as compared to conventional methods. Despite the lower reactivities, VO(OR)3 and VO(acac>2 can be employed as an oxidant, although a stoichiomettic amount is required in each case. Use of a,p-unsaturated ketones leads the different reaction routes. 2-Cyclohexen-l-ones 54 undergo dehydrogenative aromatization to give the aryl alkyl ethers 55 [105]. More than 2 equiv. of VO(OR)Cl2 are required to complete the reaction, since the oxovanadium(V) compound is a one-electron oxidant. Isophorone is also oxidatively aromatized to the aryl ether 56 with the migration of the methyl group (Scheme 2.45). 

A wide variety of high-performance polymeric materials have been synthesized by incorporating thermally stable moieties such as sulfone, ketone, or aryl or alkyl phosphine oxide in addition to the ether linkage in poly(arylene ether)s. 

Different nucleophiles such as methanol, allylsilanes, silyl enol ethers, trimethylsilyl-cyanide, and arenes can be used in this process [62]. When the sulfide itself contains an unsaturated or aromatic fragment and the process is carried out in the absence of a nucleophile, an intramolecular anodic sub-stitution/cyclization might occur [61-63]. Methyl esters of 2-benzothiazolyl-2-alkyl or aryl-acetic acid, oxidized in MeOH/Et4 NCIO4 or H2SO4 in the presence of CUCI2, form 2,2-dimethoxy products (Eq. 7) [64]. 

A plot of the temperatures required for clouding versus surfactant concentration typically exhibits a minimum in the case of nonionic surfactants (or a maximum in the case of zwitterionics) in its coexistence curve, with the temperature and surfactant concentration at which the minimum (or maximum) occurs being referred to as the critical temperature and concentration, respectively. This type of behavior is also exhibited by other nonionic surfactants, that is, nonionic polymers, // - a I k y I s u I Any lalcoh o I s, hydroxymethyl or ethyl celluloses, dimethylalkylphosphine oxides, or, most commonly, alkyl (or aryl) polyoxyethylene ethers. Likewise, certain zwitterionic surfactant solutions can also exhibit critical behavior in which an upper rather than a lower consolute boundary is present. Previously, metal ions (in the form of metal chelate complexes) were extracted and enriched from aqueous media using such a cloud point extraction approach with nonionic surfactants. Extraction efficiencies in excess of 98% for such metal ion extraction techniques were achieved with enrichment factors in the range of 45-200. In addition to metal ion enrichments, this type of micellar cloud point extraction approach has been reported to be useful for the separation of hydrophobic from hydrophilic proteins, both originally present in an aqueous solution, and also for the preconcentration of the former type of proteins. 

The resonances in the butyl ether region occur in three distinct bands. Chemical shift data for the a carbon atom resonances in about 20 ethers indicate that the resonances centered about 872.9 may result from hindered aryl ethers, for example, butyl 2,6-dimethylphenyl ether, butyl benzyl ethers, or butyl n-alkyl ethers, for example, dibutyl ether. The resonances in this region could arise from tetrahydrofuran residues in the coal product. However, the results obtained in this laboratory and in Larsen s laboratory are much more compatible with interpretations that exclude the involvement of tetrahydrofuran and focus on the reactions of the labeled butylation reagent with 2,6-disubstituted phenoxides, benzylic oxides, and primary alkoxides liberated in the formation of the coal polyanion. The most intense resonance centered at... 

Generally, arene(alkoxy)carbene chromium complexes react with aryl-, alkyl-, terminal or internal alkynes in ethers or acetonitrile to yield 4-alkoxy-l-naphthols, with the more hindered substituent ortho to the hydroxyl group . Upon treatment with alkynes, aryl(dialkylamino)carbene chromium complexes do not yield aminonaphthols, but they form indene derivatives . Vinyl(dialkylamino)carbene complexes, however, react with alkynes to yield aminophenols as the main products The solvent is one of the many factors that affects this type of reaction, for which the most important is the polarity and/or coordinating ability of the solvent. The Dotz benzannulation reaction yields either arene chromium tricarbonyl complexes or the decomplexed phenols, depending on the work-up conditions. Oxidative work-up yields either decomplexed phenols or the corresponding quinones. 

Arylthallium bis(trifluoroacetate)s are converted by successive treatment with KF and BF3 into aryl fluorides.Thallium(iii) nitrate (TTN) readily oxidizes dialkyl sulphides and selenides to the corresponding sulphoxides or selenoxides, and 2-(alkylthio)-l-arylethanones (37) into compounds (38) in methanolic solution.In a modification of the TTN oxidative conversion of aryl alkyl ketones into arylacetic acids, enol ethers derived from the ketones are used instead of the ketones themselves. This reduces the formation of side products. Cyclic aralkyl ketones (39) may be ring-expanded and alkylated to give compounds (40) via treatment of their Wittig-derived alkenes with TTN/ an extrapolation of the basic reaction discovered previously. 

If the allyl group of the aryl allyl ether featured a tri- or tetra-substituted alkene, then the thermodynamic isomerization to the aromatic benzofuran could not occur, and dihydroben-zofurans were consequently produced in good to excellent yields (Figure 9.8). As in the benzofuran systems, a host of aryl and alkyl substitution patterns were tolerated in this oxidative cyclization. A number of polycyclic and highly functionalized dihydrobenzofurans were obtained via this palladium(II)-catalysed oxidation. 

As with aryl ether substrates, we also investigated alkyl esters with alkyl groups higher than methyl. As with the higher alkyl ethers, such species undergo 1,2-H-O elimination instead of C-O oxidative addition. Ethyl acetate, for example. 

Alkyl ethers are an important subclass of compounds in natural products. The direct constmction of alkyl ethers from C(sp )-H bonds is a challenging but promising access and thus is being actively pursued. Chen et al. first addressed this unsolved difficulty. They developed a Pd(ll)-catalyzed, picolinamide-assisted functionalization of y-C(sp )-H bond with primary, secondary, and even bulky tertiary alcohols (Scheme 1.29) [73]. The perfect compatibility of simple alcohols was one of the most striking features. Furthermore, under the optimized reaction conditions, functionalization of unreactive primary C(sp )-H bond ispreferential even in the presence of secondary C(sp )-H bond. Besides C-O bond coupling, picolinamide-assisted Pd(II)-catalyzed tandem arylation and oxidation of benzylic C-H bond can dexterously construct unsymmetric diaryl ketones [74]. 

Commercially important PIj photoinitiators are aryl alkyl ketones and acylphosphine oxides. Benzoin ethers represent an important class of aryl alkyl ketones and, probably, the first class of photoinitiators used in UV curing, predominantly in the area of particle board finishing. 

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