Phenols with silver oxide

Preparation by oxidation of 2,4-di-tert-butyl-6-(p-methoxybenzyl)phenol with silver oxide in boiling acetone for 40 min (24%) [1193]. 

Several dibenzo[6,tf ]pyran-6-ones (360) have been prepared by the reaction of substituted phenols with 2-methoxycarbonyl-l,4-benzoquinone in the presence of trifluoroacetic acid (79HCA2833). Treatment with silver oxide converts the products into the related quinones which may be elaborated to benzo[6]naphtho[[Pg.800]

Phenols are more easily oxidized than alcohols, and a large number of inorganic oxidizing agents have been used for this purpose. The phenol oxidations that are of the most use to the organic chemist are those involving derivatives of 1,2-benzenediol (pyrocate-chol) and 1,4-benzenediol (hydroquinone). Oxidation of compounds of this type with silver oxide or with chromic acid yields conjugated dicarbonyl compounds called quinones. 

In relation to carbohydrate chemistry, the Koenigs-Knorr synthesis of glycosides involves the treatment of glycosyl halides with an alcohol or phenol in the presence of a heavy metal salt.267 Karrer268 discovered that reaction of silver salts of hydros acids could also be used and use of these reagents has been extended more recently. Numerous variations and improvements on the original method have now been reported, and silver oxide, silver carbonate or silver trifluoromethanesulfonate have since become the accepted standard reagents.267... 

Oxidation procedure. The reagent is freed from residual water by azeotropic distillation with benzene (CAUTION). The compound to be oxidised is then added and refluxed in benzene (c. 200ml for 0.5-2.0g of compound). At the end of the reaction (determined by t.l.c. monitoring), the solid phase is filtered off and the solvent evaporated. The product is usually highly pure and recrystallisation is unnecessary. With 2,6-dimethylphenol the molar ratio of phenol to silver carbonate is 1 4.4, and the reaction time is half an hour in this case 3,3, 5,5 -tetramethyldiphenoquinone is obtained in 98 per cent yield and has m.p. 217-218 °C. With 2,4,6-trimethylphenol, using the same molar ratio of phenol to oxidant, and a reaction time of 2 hours, 3,3, 5,5 -tetramethylstilbenequinone is obtained in 93 per cent yield and having m.p. 227-228 °C. 

The simpler architecture is the 1,1 -biphenyl scaffold, likewise introduced by Hoveyda and coworkers [19]. The synthesis of the imidazolium salt starts with a chiral diamine and a substituted, achiral biphenyl [82-84], Subsequent introduction of a Mes substituent on the remaining primary amino end and ring closure reaction yields the chiral saturated imidazolium salt after hydrolysation of the methoxy group to liberate the phenolic hydroxy group (see Figure 4.22). Reaction with silver(I) oxide and carbene transfer to a Grubbs (Hoveyda) catalyst sets up the ruthenium catalyst complex. 

Chiral 4-hydroxy-2-cyclopentenones. Both (R)- and (S)-4-hydroxy-2-cyclo-pentenones can be obtained from phenol. The first step is alkaline hypochlorite oxidation to the acid 1, which is resolved with brucine. Oxidative decarboxylation of 1 gives 2, which is partially dechlorinated and protected as the silyl ether (3). The last step to 4 is reduction with zinc-silver (S, 760) or zinc-copper. ... 

Sulfonic esters are most frequently prepared by treatment of the corresponding sulfonyl halides with alcohols in the presence of a base. This procedure is the most common method for the conversion of alcohols to tosylates, brosylates, and similar sulfonic esters. Both R and R may be alkyl or aryl. The base is often pyridine, which functions as a nucleophilic catalyst, as in the similar alcoholysis of carboxylic acyl halides (16-61). Propylenediamines have also been used to facilitate tosylation of an alcohol. Silver oxide has been used, in conjunction with KI. Primary alcohols react the most rapidly, and it is often possible to sulfonate selectively a primary OH group in a molecule that also contains secondary or tertiary OH groups. The reaction with sulfonamides has been much less frequently used and is limited to A,A-disubstituted sulfonamides that is, R— may not be hydrogen. However, within these limits it is a useful reaction. The nucleophile in this case is actually RO . However, R may be hydrogen (as well as alkyl) if the nucleophile is a phenol, so that the product is RS020Ar. Acidic catalysts are used in this case. Sulfonic acids have been converted directly to sulfonates by treatment with triethyl or trimethyl orthoformate, HC(OR)3, without catalyst or solvent and with a trialkyl phosphite, P(OR)3. ... 

Huysmans and Waters (1966) have combined heterogeneous oxidation with a flow technique by passing solutions of phenols in benzene through a bed of solid silver oxide or lead dioxide held in a tube in the cavity of the spectrometer. 

Koenigs-Knorr synthesis. Formation of glycosides from acetylated glycosyl halides and alcohols or phenols in the presence of silver carbonate or silver oxide. The reaction proceeds with inversion of configuration. 

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