Acyl iodides

Wilkinson s catalyst has also been reported to decarbonylate aromatic acyl halides at 180°C (ArCOX ArX). This reaction has been carried out with acyl iodides, bromides, and chlorides. Aliphatic acyl halides that lack an a hydrogen also give this reaction, but if an a hydrogen is present, elimination takes place instead (17-16). Aromatic acyl cyanides give aryl cyanides (ArCOCN—> ArCN). Aromatic acyl chlorides and cyanides can also be decarbonylated with palladium catalysts. °... 

Subsequent insertion of CO into the newly formed alkyl-ruthenium moiety, C, to form Ru-acyl, D, is in agreement with our 13C tracer studies (e.g., Table III, eq. 3), while reductive elimination of propionyl iodide from D, accompanied by immediate hydrolysis of the acyl iodide (3,14) to propionic acid product, would complete the catalytic cycle and regenerate the original ruthenium carbonyl complex. 

In the case of nonracemic homopropargylic ether 17, hydrozirconation/carbonylation was followed by exposure of the intermediate to molecular iodine (Scheme 4.12) [39]. The ( )- and (Z)-forms of the acyl iodide presumed to be formed in situ were seemingly in equilibrium under the reaction conditions and intramolecular attack followed by dealkylation afforded (S)-(+)-parasorbic acid. 

Reaction of the 2-phenyl-4-(phosphoranylidene)-5(47/)-oxazolone 219 with alkyl halides gives 4-alkyl-2-phenyl-5(47/)-oxazolones 220 in good yields. Reaction of 219 with acyl iodides or bromides gives C-4- or O-acyl products 221 or 222. Reaction of 219 with acyl chlorides gives 4-(l-chloroalkylidene)-2-phenyl-5(47/)-oxazolones 224 that are Wittig-like products. The use of benzoyl fluoride gives rise to 4-(l-benzoyloxybenzylidene)-2-phenyl-5(47/)-oxazolone 223. These reactions are summarized in Scheme 7.68. 

An attempt was also made to produce 0-iodo acyl iodides by the reaction of iodine, carbon monoxide and olefins in the presence of palladium or platinum chloride. This is, in effect, an attempt to make Dr. Tsuji s reaction catalytic rather than stoichiometric. No carbonyl insertion occurred at 1 atm. of carbon monoxide. However, it was found that iodination of the olefin was catalyzed by platinum olefin complexes and that an additional increase in catalytic activity accompanied the presence of carbon monoxide. There has been much speculation at this conference concerning the possibility of affecting catalytic activity by changing the ligands in the coordination sphere of the catalyst. This would appear to be such a case. 

Carboxylic acids and some of their derivatives react with diiodosilane SiH lj to give good yields of acyl iodides Keinan Sahai J. Org. Chem. 1990, 55, 3922. 

Cleavage of ethers. A few reports have mentioned that acyl iodides can cleave ethers in the absence of a Lewis acid. Since acyl iodides are not readily available, Oku et al. have used Nal and an acyl chloride as a possible equivalent. In any case, the system does cleave both cyclic and acyclic ethers selectively at the less substituted a-C—O bond. Although any acyl chloride can be used, use of pivaloyl chloride is particularly attractive because the resulting pivaloyl esters are readily hydrolyzed. Indeed this system is particularly useful for deprotection of methyl ethers. 

Acyl iodides.1 This reagent converts acyl chlorides into acyl iodides at 25°. In combination with iodine (1 1) it also converts carboxylic acids, esters, and anhydrides into acyl iodides in generally high yield. This reaction in combination with an alcohol is a useful method for transesterification of hindered alcohols. 

Such a reactivity has been observed previously during the pyridine-promoted solvolysis of acetyltetracarbonyl cobalt(I) (56). Both effects in the case of ruthenium suggest that the carbonylated product does not leave the metal center by reductive elimination of acyl iodide, but rather by nucleophilic displacement. 

Acyl iodides RCOI add to [Rh(CO)2I2] to give [RC(0)Rh(C0)2I3] which readily loses CO. The Pr"CO and Pr CO complexes equilibrate via decarbonylation and isomerization steps.53... 

Acyl iodides. Aliphatic and aromatic acyl iodides and diacyl iodides can be prepared from the corresponding chlorides by reaction with anhydrous Nal in absolute acetonitrile, and isolated by liquid-liquid extraction with pentane, which is almost immiscible with acetonitrile. The products can be stored under N over copper powder as stabilizer. The same technique can be used to obtain iodoglyox.ilic esters, ROOCCOl, and iodoformic esters, ROCOl. ... 

The mechanism has been extensively studied by Forster and coworkers at Monsanto and is shown in Scheme 19. It is actually a double catalytic cycle involving the Hl-catalyzed conversion of MeOH to Mel and H2O at the beginning of the Rh-catalyzed carbonylation reaction, and regeneration of HI at the end of the Rh cycle by hydrolysis of the acyl iodide. 

One pathway involves reaction of methyl acetate with HI to produce Mel and acetic acid. The Mel is carbonylated by [Rh(CO)2l2] to give acyl iodide, which can then react with acetic acid to produce acetic anhydride and regenerate HI. 

Interchange of halogen is a means of synthesis of certain acyl halides which cannot be conveniently prepared by other methods. Acetyl fluoride is made from acetyl chloride and sodium hydrogen fluoride in acetic anhydride solution." By passing a stream of hydrogen bromide through oxalyl chloride an 85% yield of oxalyl bromide, (COBr), is obtained. The bromide cannot be made by the action of phosphorus pentabromide on oxalic acid. The method has also been applied to the preparation of acetyl bromide and iodide and other acyl iodides. ... 

For a review, see AnseU, M.F., in Patai, S. The Chemistry of Acyl Halides, Wiley, NY, 1972, pp. 35-68. Carboxyhc acids and some of their derivatives react with diiodosilane SiFt2l2 to give good yields of acyl iodides Keinan, E. Sahai, M. J. Org. Chem. 1990, 55, 3922. 

The quite labile acyl isocyanides on the other hand may be obtained from acyl iodides with AgCN in CH2CI2 similarly imidoyl bromides give rise to imidoyl isocyanides (Scheme 25). Both types of compounds decompose quite easily under comparatively mild conditions. Acyloxy isocyanides are well known too. ... 

TABLE XIII. ORGANIC DERIVATIVES OF ACYL HALIDES IV. Acyl Iodides. Liquids I) (Listed in order of increasing atmospheric b.p. ) ... 

TABLE XIII. ORGANIC DERIVATIVES OF ACYL HALIDES IV. Acyl Iodides. Liquids... 

Scheme 30 Proposed catalytic cycle for methanol carbonylation to acetic acid (Monsanto process). Acyl-iodide reductive elimination from a Rh(ni) center is the key step toward the product formation...

Acyl iodides are also available from acid chlorides and TMS-I Schmidt, A. N. Russ, M. Grosse, D., Synthesis 1981, 216. 

Organic groups in organocobalt complexes are usually cleanly cleaved by iodine. Acylcobalt tetracarbonyls give acyl iodides, apparently in high yield (5). 

The mechanism of this reaction was investigated to find out if carbon monoxide dissociation is the rate-determining step (16). The rate of the reaction of acetylcobalt tetracarbonyl with iodine is too fast to measure under conditions which allow dissociation rate to be measured easily. Thus, dissociation is not rate-determining, and the acylcobalt tetracarbonyl and the iodine must be reacting directly. Further studies with the less reactive acyl(triphenylphosphine)cobalt tricarbonyls showed that the first step in the reaction with iodine is a rapid cleavage of the cobalt-carbon bond to form acyl iodide and iodo(triphenylphosphine)cobalt tricarbonyl. 

The acyl group RCO is a hard Lewis acid, hence its combination with hard bases forms thermodynamically stable molecules, e.g., carboxylic acids RCOOH, esters RCOOR, and amides RCONR2. In contrast, its union with soft bases results in highly reactive or labile species such as thioesters RCOSR, selenoesters RCOSeR, and acyl iodides RCOI. 

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