Silver benzoate

Esters of the homologous acids are prepared by adding silver oxide in portions rather than in one lot to a hot solution or suspension of the diazo ketone in an anhydrous alcohol (methyl, ethyl or n-propyl alcohol) methanol is generally used and the silver oxide is reduced to metallic silver, which usually deposits as a mirror on the sides of the flask. The production of the ester may frequently be carried out in a homogeneous medium by treating a solution of the diazo ketone in the alcohol with a solution of silver benzoate in triethylamlne. 

Example—o 3652 grm. silver benzoate gave o lgao gim. siher. 

The structure of 82 was established by alkaline ring cleavage to benzilic acid amide and by hydrogenolysis to (C6H5)2CH—CONH— COCfiHs. These reactions also served to eliminate 83 as the structure of the 169° compound. The other possible isomeric structure, (C6H5)2C(CN)0C0C6H5, which could have formed after 0-acylation, was ruled out by its independent synthesis from bromodiphenyl-acetonitrile and silver benzoate. 

Suitable substrates for the Hunsdiecker reaction are first of all aliphatic carboxylates. Aromatic carboxylates do not react uniformly. Silver benzoates with electron-withdrawing substituents react to the corresponding bromobenzenes, while electron-donating substituents can give rise to formation of products where an aromatic hydrogen is replaced by bromine. For example the silver /)-methoxybenzoate 6 is converted to 3-bromo-4-methoxybenzoic acid 7 in good yield ... 

Although the Wolf rearrangement of diazoketones in the presence of silver benzoate and triethylamine in methanol could involve rearrangement of an intermediate diradical or carbonium ion conjugate... 

Silver salt. C7H5Ag02, silver benzoate. Light-sensitive powder. Sol in 385 parts cold water, more sol in hot water very slightly sol in ale. 

Sebacid acid dinitrile, 50, 20 SELECTIVE o-BROMINATION OF AN ARALKYL KETONE WITH PHENYL-TRIMETHYL AMMONIUM TRIBROMIDE 2-BRQM0ACETYL-6-METH-OXYNAPHTHALENE AND 2,2-DI-BROMOACETYL-6-METHOXYNAPH-THALENE, 53, 111 Shikimic acid, 50, 27 Silver benzoate, as catalyst in decomposition of diazoketones, 50, 78... 

The equivalence of sulfur and oxygen in this ring system carries over to NSAIDs as well. Preparation of the sulfur analogue of isoxepac (6-4) starts with the alkylation of thiophenol (27-1) with benzyl chloride (26-1). Cyclization of the intermediate thioether (27-2) then affords the homothioxanthone (27-3). The carboxyl side chain is then extended by means of the Amdt-Eistert homologation reaction. The acid is thus hrst converted to its acid chloride by means of thionyl chloride. Reaction with excess diazomethane leads to the diazoketone (27-4). Treatment of that intermediate with silver benzoate and triethylamine leads the ketone to rearrange to an acetic acid. There is thus obtained tiopinac (27-5) [28]. 

The same result can be achieved in one step with m-chloroperoxybenzoic acid and water.719 Overall anti addition can also be achieved by the method of Prevost. In this method the olefin is treated with iodine and silver benzoate in a 1 2 molar ratio. The initial addition is anti and results in a 3-halo benzoate (71). These can be isolated, and this represents a method of addition of IOCOPh. However, under the normal reaction conditions, the iodine is replaced by a second PhCOO group. This is a nucleophilic substitution reaction, and it operates by the neighboring-group mechanism (p. 308), so the groups are still anti ... 

Esters can be formed by the use of various alcohols as solvent with silver benzoate while silver trifluoroacetate in THF/H20 leads to the formation of free (3-amino acids. This approach has been used to form peptide 5 (Scheme 4). In this case, the alcohol solvent is replaced by an alternative nucleophile dissolved in THF. Hence, concomitant peptide coupling is achieved when the nucleophile is a peptide with a free N-terminus. 

Fuming or concentrated nitric acid eliminates the iodine from the di-iodide, white crystals of the b dinitrate, (CH3)2Te(N03)2, being deposited.3 These melt sharply without decomposition at 142° C. The di-iodide gives a green platinum salt with chloroplatinic acid. With silver benzoate it forms a benzoate, white needles, M.pt. 154° C., and the yellow picrate, obtained in a similar manner, crystallises... 

The syn- and anfi-diol epoxides of benz[a] anthracene and benzo[a] pyrene have been prepared from dihydroarenes by sequential Prevost reaction with silver benzoate-iodine, dehydrogenation, methanolysis, and epoxidation, e.g.,... 

Treatment of A-1 -phcnyl-2-butcnc 5 with I2 and silver benzoate (1 2) followed by saponification gives an equal mixture of [2.S ,3A -l-phenyl-2,3-butanediol and 12 A ,3. S -1 -phenyl-2,3-butancdiol. Treatment of 5 with I2 and silver acetate in the presence of water followed by saponification gives an equal mixture of [2A ,3A -1-phenyl-2,3-butancdiol and [2.S ,3.S -1-phenyl-2,3-butanediol. Determine the stereochemistry for these two processes. Can you account for the difference mechanistically ... 

Silver nitrate White precipitate of silver benzoate from cold solutions soluble in hot water and also in dilute ammonia solution... 

The reaction of diazoketone 621 with either silver benzoate in methanol or with rhodium acetate in dichloromethane led to the formation of the stable azetinium salt 622, which was isolated as yellow crystals (Equation 236) <1998AGE2229>. 

Numerous conditions have been developed for this transformation, but reproducible yields have usually been obtained by mixing a silver salt with a coreagent, such as silver nitrate associated with wet ammonia, silver oxide with triethylamine or sodium thiosulfate, and silver benzoate with triethylamine. Nonbasic conditions have also been described by Koch and Podlech using silver trifluoroacetate deposited on silica.6 These modifications have been developed for the homologation of Fmoc-protected amino acids. 

Since ketene is probably the intermediate of the Wolff rearrangement, the choice of solvents dictates the nature of the product. Indeed, water gave carboxylic acids, whereas alcohols or amines led to esters and amides, respectively. These combinations have been applied to the synthesis of more complex molecules. For example, the total synthesis of carbonolide B, a 16-membered macrolide antibiotic, relied on Amdt-Eistert homologation. In this sequence, a protected furanuronic acid was transformed to the corresponding a-diazoketone, which was then converted to its homologous carboxylic ester. The reaction was achieved using catalytic amounts of silver benzoate and excess of triethylamine in methanol (Scheme 3.4).11... 

Silver benzoate in methanol is also the catalyst of choice for the classical homologation of cr-amino acids (and peptides) to the corresponding f3-amino esters by Wolff rearrangement.353 An interesting application in natural... 

The UCST for acetonitrile + water mixtures is sensitive to added salt (Renard and Heichelheim, 1967 Benter and Schneider, 1973 Model and Schneider, 1971), some salts (e.g. sodium benzoate) increasing, others (e.g. silver benzoate) lowering the UCST. Coetzee and Campion (1967) have shown that chloride, bromide and iodide... 

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