Arylations silver® oxide

Alkaline silver oxide is the most satisfactory reagent for oxidation of the aldehyde 3 to the acid 4.2 This reagent has been recommended for oxidation of aryl aldehydes (1,1012-1013), but only moderate yields have been reported for oxidation of a,/ -enals with Ag20.3 Apparently, the successful results in the oxidation of 3 are the result of the activating effect of the keto group. 

The reaction can be performed at room temperature with various heteroaryl halides (Equation 73) <20050L697>. It was found that (2-pyridyl)allyldimethylsilanes are pyridyl-transfer reagents in palladium-catalyzed coupling reactions of aryl iodides in the presence of silver oxide as an activator <20060L729>. 

Applications of this reaction are not limited to advanced materials, but can be applied to natural product synthesis. Indeed, indoles have quite recently (in 2008) been arylated in the presence of palladium acetate and silver oxide (Scheme 10.52).84... 

Conditions based on stoichiometric amounts of silver oxide have been developed by Mori et al. for the synthesis of arylated alkynes from terminal alkynes and aryl iodides. Under such conditions, neither silylated alkynes nor aryl bromides or triflates did not undergo coupling (Scheme 10.78).129,130... 

The classical Hunsdiecker reaction (equation 18), involving the reaction of silver caiboxylates widi halogens, and the various associated side reactions, has been reviewed several tunes. Optimum yields are obtain widi bromine, followed by chlorine. Iodine gives acceptable yields provid diat the correct stoichiometry of 1 1 is used. The reaction is most frequently carried out in tetrachloromediane at reflux. From a practical pmnt of view, one drawback is the difficulty encountered in the preparation of dry silver caiboxylates the reaction of silver oxide on the acyl chloride in tetrachloromediane at reflux has been employed to circumvent diis problem. Evidendy the use of molecular bromine limits die range of functional groups compatible widi die reaction the different reaction pathways followed by the silver salts of electron poor (equation 19) and electron rich (equation 20) aryl carboxyl s illustrate this point well. 

Alkylation of2-aryl-I, 4-oxadiazoles. Alkylation of 2-aryl-l,3,4-oxadiaaoles (I) by alkyl halides in acetonitrile in the presence of silver oxide gives O- and N-alkyl... 

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. ... 

Matsubara and Yoshida have shown that 9,10-di(pentafluorophenyl)anthra-cene can be synthesized by a copper-catalyzed arylation of pentafluorobenzene with dibromoanthracene [105], The reaction is only successful if silver oxide base is used. 

Aryl carboxamides can be converted to the respective nitriles by treatment with silver oxide (Ag20) and iodoethane in benzene under non-acidic conditions in good yields of 50-93% [1144],... 

Oxidation of a-amino-acids with silver(ii) picolinate gives almost quantitative yields of nor-aldehydes silver oxide causes further oxidation to the nor-acid. The possibility is suggested of the simultaneous operation of a radical mechanism in solution and a two-electron shift process at the solid silver salt surface. Aryl alkanes and aryl alkanols are oxidized by silver(ii) picolinate to aldehydes and ketones, a-Aminoketones are dehydrogenated by mercury(ii) salts to ketones iminium ions, such as (139), are postulated as intermediates (Scheme 58). 

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