Aromatic ethers, oxidations

Oxidation of side chains. The oxidation of halogenated toluenes and similar compounds and of compounds with side chains of the type —CHjCl and —CH OH proceeds comparatively smoothly with alkaline permanganate solution (for experimental details, see under AromcUic Hydrocarbons, Section IV.9,6 or under Aromatic Ethers, Section IV,106). The resulting acid may be identified by a m.p. determination and by other teats (see Section IV,175). 

TRAHANOVSKY Ether oxidation Oxidation of aromatic ethers to carbonyl compounds with cemim ammonium nitrate... 

Aromatic ethers and furans undergo alkoxylation by addition upon electrolysis in an alcohol containing a suitable electrolyte.Other compounds such as aromatic hydrocarbons, alkenes, A -alkyl amides, and ethers lead to alkoxylated products by substitution. Two mechanisms for these electrochemical alkoxylations are currently discussed. The first one consists of direct oxidation of the substrate to give the radical cation which reacts with the alcohol, followed by reoxidation of the intermediate radical and either alcoholysis or elimination of a proton to the final product. In the second mechanism the primary step is the oxidation of the alcoholate to give an alkoxyl radical which then reacts with the substrate, the consequent steps then being the same as above. The formation of quinone acetals in particular seems to proceed via the second mechanism. ... 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

Such a pre-equilibrium closely parallels that suggested by Dewar et for the manganic acetate oxidations of several aromatic ethers and amines (p. 405). Other features of the reaction are a p value of —0.7 and identical activation energies of 25.3 kcal.mole for oxidation of toluene, ethylbenzene, cumene, diphenylmethane and triphenylmethane. 

CgHsCl as in the absence of aromatic, suggesting auto-decomposition of the oxidant as the slow step (p. 386). The oxidation of toluene was somewhat faster, implying an additional electron-transfer pathway (c/. the oxidation of aromatic ethers and amines, p. 405). 

Friedel-Crafts acylation of aromatic ethers has been performed in the presence of a variety of metal chlorides and oxides (FeCl3, ZnCl2, A1C13, Fe203, Fe304, etc.) but without temperature control [52], Scheme 10.8. 

Several elegant syntheses of anthra-cyclinone aglycons are based on the ability to intercept the intermediate radical cation (76) formed from the oxidation of aromatic ethers (75) and (79) in situ with alkanols [9, 44, 45]. Inter- and intramolecular capture can occur. As illustrated in Scheme 19, the methodology leads to the facile construction of substituted quinone mono- and bisketals. 

Low molecular weight aromatic ethers have been prepared principally by the condensation of phenolate salts with aromatic halides 82). The Ullmann condensation (81), which employs copper or its salts as catalysts has been used in most cases in the laboratory. Recently a modification of the Ullmann condensation which consists of heating copper (1) oxide, the free phenol, and the aromatic halide in s-collidine has been reported (3). This method is recommended for alkali-sensitive aromatic compounds. In addition, reaction of phenolate salts with copper (1) oxide and the aromatic halide in boiling N,N-dimethyl formamide is described. When the halogen is activated by electronegative groups as in -chloroni-... 

Aromatic ethers are notable for their exceptional thermal, oxidative, and hydrolytic stability. Because of this stability they have been synthesized for use as high temperature fluids (28, 72). 

The polymerization of cyclohexane 1.4-oxide has been described (87). A high melting, high molecular weight polymer was obtained. It is conceivable that this polymer could be dehydrogenated to the aromatic ether, however, no information is available on this point. 

BTIB oxidations of aromatic ethers in which sulfido groups are tethered to the ring provide access to heterocyclic sulfides [64], while related oxidations of azido-tethered analogs lead to quinone imines and/or their dimethyl ketals... 

Note Confirmed human carcinogen Nonpolar, aromatic solvent sweet odor very flammable and toxic confirmed human carcinogen soluble in alcohols, hydrocarbons (aliphatic and aromatic), ether, chloroform, carbon tetrachloride, carbon disulfide, slightly soluble in water incompatible with some strong acids and oxidants, chlorine trifluoride (zinc in the presence of steam) decomposes at high temperature to form biphenyl. Synonyms cyclohexatriene, benzin, benzol, phenylhydride. These are the most common, although these are many other synonyms. 

BTIB-oxidations of aromatic ethers can also be directed to C,C-bond formation. Intermodular examples include oxidative heterocouplings of 1,4-dimethoxybenzene with /1-dicarbonyl compounds, presumably via their enol tautomers, to the arylated /1-dicarbonyl derivatives 102... 

A novel use of this general method is the addition of an aromatic nitrile oxide to the nitrile equivalent tied up in the triazine (184). The reaction occurs to give a good yield only in the presence of boron trifluoride etherate whose role is illustrated in Scheme 18 (78BCJ1484).. ... 

The chiral induction of carbohydrate enol ethers in 1,3-DC with some aromatic nitrile oxides was investigated. The highest diastereoseletivity (28 1 dr) was achieved with a 3-0-vinyl-p-D-fructopyranose derivative and 2,4,6-trimethylbenzonitrile oxide <02TA2535>. 

A practical synthesis of 1,3-OX AZEPINES VIA PHOTOISOMERIZATION OF HETERO AROMATIC V-OXIDES is illustrated for 3,1-BENZOXAZEPINE. A hydroboration procedure for the synthesis of PERHYDRO-9b-BORAPHENALENE AND PERHYDRO-9b-PHEN-ALENOL illustrates beautifully the power of this methodology in the construction of polycyclic substances. The conversion of LIMONENE TO p-MENTH-8-EN-YL METHYL ETHER demonstrates a regio-and chemoselective method for the PHOTOPROTONATION OF CYCLOALKENES. An efficient method for the conversion of a ketone to an olefin involves REDUCTIVE CLEAVAGE OF VINYL PHOSPHATES. A mild method for the conversion of a ketone into the corresponding trimethylsiloxy enol ether using trimethylsilyl acetate is shownforthe synthesis of (Z)-3-TRIMETHYLSILOXY-2-PENTENE. 

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