Rearrangements silver® acetate

The first example of a methoxy-group participation in sugars was reported by Lemieux and Fraser-Reid 7) who observed 1,3,4,6-tetra-O-acetyl-2-0-methyl-D-glucop3U-anose (4) as one of the products of bro-minolysis of methyl 3,4,6-tii-0-acetyl-2-deoxy-2-iodo- -D-mannopyra-noside ffj in the presence of silver acetate. The cyclic methoxonium ion (2) was indicated to be an intermediate in this rearrangement, giving rise to the product either by direct nucleophilic attack of acetate ion or... 

Lemieux and Brice33 have studied the rearrangement under the conditions employed by Pacsu,80 involving the use of stannic chloride as catalyst, with pure chloroform as solvent. The reaction was shown to be specific for the anomeric center, and the following observations appear to establish definitely the main features of the mechanism for this reaction. A quantitative yield of silver chloride was obtained on treating silver acetate with an excess of stannic chloride in chloroform, and it seemed probable that there results a chloroform solution of stannic chloride and stannic trichloride acetate (LVIII). The solution was able to catalyze the anomerization. 

The silver(I)-mediated electrocyclic ring opening of halocyclopropanes has been used to induce extensive skeletal rearrangements in gcm-dibromospiropentanes, providing rapid construction of naphthalenes and/or indenes (Scheme4.21 ).34 A variety of Lewis acids, Brpnsted acids, and solvent effects were carefully examined before optimal conditions were identified. It was found that subjection of spirocycle 60 to silver acetate in trifluoroacetic acid afforded rearrangement products 61 and 62 in moderate to good yields. The proposed mechanism of the reaction is illustrated in Scheme 4.21. 

Acids or salts are utilized directly in Stephen s method 166 (iii) reaction with 3-chlorobenz[d]isothiazole-1,1-dioxide (6) (pseudosaccharin chloride3,166). The initial step is presumably formation of 29, followed by Mumm rearrangement. Frequently one obtains pseudosaccharin anhydride (32)25,162 as a by-product. From the reactions with silver acetate and below 3° only A-acetylsaccharin (33) besides 32 was isolated.167 In this context reexamination of the reported 3-O-benzene-sulfonylbenz[d] isothiazole-1,1-dioxide42 and the supposed 3-O-benzoyl... 

A number of biomimetic syntheses have included Wagner-Meerwein rearrangements. A chemical conversion of humulene (48) to sterpurene (50) involved an interesting series of Wagner-Meerwein rearrangements (see Scheme 19).- - Humulene (48) was converted to the cyclooctenol (51) and thence to the bromide (52) via the protoilludyl cation (49). Treatment of (52) with silver acetate in acetic acid gave racemic sterpurene (50). In contrast the epimeric bromide (53) gave (54). 

Using an alternative method, homoallylic iodides are efficiently transformed into cyclopropylmethyl acetates using silver acetate in anhydrous benzene (Table 1). y-Disubstituted or conjugated homoallylic iodides are particularly reactive and rearrange quantitatively. y-Monosub-stituted iodides afford mixtures of cyclopropylmethyl and homoallyl acetates in a 1 1 ratio, whereas the absence of a y-alkyl or aryl group in the homoallylic iodides leads to elimination, only. 

Rearrangement. Benn2 used silver perchlorate in refluxing acetone to rearrange the acetate of the ethynylcarbinol (4) to the isomeric allenes (5 and 6). Configurations were assigned on the basis of optical rotatory dispersion and NMR spectra. 

One of the most general approaches to the synthesis of this type of compounds involves the Lewis acid promoted rearrangement of acetals of a-substituted propiophenones [4,5]. Besides silver salts, a large variety of soft and borderline Lewis acids have been found to be convenient catalysts for the 1,2-aryl shift, noticeably zinc halides in substoichiometric amounts [6]. As final products need to be free of metal traces for human consume, the use of Lewis acids supported on microporous solids can be advantageous since a better recovering of the catalyst can be anticipated. 

SUica gels, 110, 221, 229, 339, 345, 416, 461,505,509 a-Siloxyallylsilanes, 485 Silver acetate, 441-442 Silver carbonate, 441 Silver carbonate-Celite, 441-442 Silver chromate-iodine, 442 Silver cyanide, 442 Silver fluoride, 161 Silver nitrate, 247 Silver(I) oxide, 441, 442-443 Silver tetrafluoroborate, 443-444 Silverll) trifluoroacetate, 444-445 Silver(II) trifluoroacetate, 527 Silylation, 227 Silyl cyclopropanes, 307 Silyl enol ethers, 127, 172, 218, 227, 296, 378, 446, 485, 524-525 Silylvinyl triflates, 410 Simmons-Smith reagent, 172,445 Smiles rearrangement, 243 Sodium, 445... 

In both cases studied using G 56-adamantanes as starting materials rearranged products were observed where oxonium ions occurred as intermediates, namely on treatment of 4°l l,8°l l-diiodo-2,6-dioxa-adamantane (J 2.1.2.1.) and N(6)-phenylsulfonyl-4N(6)8N(S),diiodo.2 -oxa-6-aza-adamantane (47 2.1.5.2.) with silver acetate in acetic acid, see G 36 - G 38 (oxonium ion) - G 39 (adamantane) + G 40 (isotwistane) ... 

Silver nitrate-catalysed rearrangements in methanol of dibromocyclopropyl propellanes have been examined. For example, (80 R = Br) gave a mixture of the corresponding methyl ketal (80 R = OMe) and bicyclo[5,4,0]undec-l(7)-en-2-one, together with minor products. One step in a reported synthesis of 1,7-methano-[12]annulene involved addition of dibromocarbene to tricyclo[4,4,l,0 ]undeca-3,8-diene (81) followed by silver acetate-catalysed ring-opening of the resultant bis-dibromocarbene adduct to give a mixture of isomeric acetates. ... 

Rearrangements. Regioselective ring contractions are possible via hromination of cyclobutyl ketones. The intermediate bromo ketone, when treated with silver acetate in acetic acid (120 °C, 6 h), affords a mixture of the cyclopropyl ketone and the acetoxy ketone (57% and 28% isolated yield, respectively, eq2).2... 

Arylhydrazinopyridines do not undergo the benzidine rearrangement . They are easily oxidized to azo compounds, even by air. Preparatively the oxidation has been effected by alkali , mercuric oxide " , and by nitrous acid in acetic acid 2a, c, Surprisingly, 3,3, 5,5 -tetranitro-2,2 -hydrazopyridine is oxidized by silver acetate to 3,5-dinitropyridine 26 2-Arylhydrazinopyridine 1-oxides give 2-arylazopyridine 1-oxides in alkali, but boiled in alcohol or acetic acid they form 2-arylazopyridines . Recrystallization of 4,4 -hydrazopyridine l,T-dioxide picrate causes oxidation to the azo compound <. Arylhydrazinopyridines are reduced to the two primary amines by zinc and hydrochloric acid < ... 

The silver-nitrate-catalysed cyclopropyl-allyl rearrangement of (451) has been used in the preparation of benzazocines and, by ring expansion of (452) with silver acetate-acetic acid, the two substituted trflns,cis-cyclonona-dienes have been made. The trans,trflns-cyclodecadienes (454), which are involved in a synthesis of cyclodeca l,6-diyne-3,8-diol, have been prepared by... 

Reactions of (145) with potassium permanganate, performic acid, aqueous lithium carbonate, and silver acetate in acetic acid are described. Treatment of the cyclopentadiene-methyl a-bromovinyl sulphone adduct with sodium methoxide in dimethyl sulphoxide gives (141) by the Ramberg-Backlund rearrangement, but in refluxing aqueous 2N sodium hydroxide (146) is also formed. Good evidence in the latter case is presented for a homolytic mechanism. With added isopropyl alcohol, in addition to (146), products are obtained by hydrogen-atom abstraction. 

Ethynyl carbinols rearrange to conjugated unsaturated aldehydes. Copper or silver salts cataly2e isomeri2ation of the acetate to an aHenic acetate, which can be hydroly2ed to an unsaturated aldehyde (204). 

Silver trifluoroacetate is a suitable catalyst for various cationic rearrangements involving multiple carbon-carbon bonds [49 5(1] In the presence of silver trifluoroacetate, 2 propynyl acetates rearrange to the butadienyl acetates to give dienes that are useful in Diels-Alder reactions [49] (equation 22)... 

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 rearrangement of the 5-cyano-4,5-dihydro-l//-azepine (93) to furo[2,3-6]pyridine (95 Scheme 9) with sodium nitrate in glacial acetic acid or with silver nitrate in aqueous ethanol proceeds by initial protonation at either C-3 or C-6 followed by hydrolysis to the cyanooctanedione ester (94). By carrying out the rearrangement with an acid ion exchange resin it is now possible to isolate the dione ester (77CJC4061). Likewise, the hydrolysis of the tetrahydro-2-benzazepine (96) to an 0 -(anilinoalkyl)benzophenone is an example of proton attack at the /3 -carbon of the enamine system (77JA5045). 

Butadienyl acetates. These useful Diels-Aldcr dienes (2) can be obtained by isomerization of 2-propynylic acetates (1) with this silver salt or with PdCl2. The substrates (1) rearrange to allcnyl acetates (3) with CuCl. ... 

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