Decarboxylation reactions Hunsdiecker reaction

Decarboxylation. Bromodecarboxylation (Hunsdiecker reaction) of a,/3-unsaturated carboxylic acids was achieved employing IBD or IBDA as catalysis. Manganese(II) acetate and lithium acetate (eq 33) can also catalyze this kind of reaction. 

Silver carboxylates 1 can be decarboxylated by treatment with bromine, to yield alkyl bromides 2 in the so-called Hunsdiecker reaction. ... 

The Hunsdiecker reaction is the treatment of the dry silver salt of a carboxylic acid with bromine in carbon tetrachloride. Decarboxylation occurs, and the product isolated is the corresponding organic bromide 16). Since dry silver salts are tedious to prepare, a modification of the reaction discovered by Cristol and Firth (77) is now... 

Reaction between diazonium salts and CuCl or CuBr (Sandmeyer) Decarboxylative halogenation (Hunsdiecker)... 

A related method for conversion of carboxylic acids to bromides with decarboxylation is the Hunsdiecker reaction.276 The usual method for carrying out this transformation involves heating the carboxylic acid with mercuric oxide and bromine. 

The decarboxylation of carboxylic acid in the presence of a nucleophile is a classical reaction known as the Hunsdiecker reaction. Such reactions can be carried out sometimes in aqueous conditions. Man-ganese(II) acetate catalyzed the reaction of a, 3-unsaturated aromatic carboxylic acids with NBS (1 and 2 equiv) in MeCN/water to afford haloalkenes and a-(dibromomethyl)benzenemethanols, respectively (Eq. 9.15).32 Decarboxylation of free carboxylic acids catalyzed by Pd/C under hydrothermal water (250° C/4 MPa) gave the corresponding hydrocarbons (Eq. 9.16).33 Under the hydrothermal conditions of deuterium oxide, decarbonylative deuteration was observed to give fully deuterated hydrocarbons from carboxylic acids or aldehydes. 

Decarboxylativehalogenation (12,417). The Hunsdiecker reaction is not useful for aromatic acids, but decarboxylative halogenation of these acids can be effected in useful yield by radical bromination or iodination of the thiohydroxamic esters, as reported earlier for aliphatic acids.1 Thus when the esters 2 are heated at 100° in the presence of AIBN, carbon dioxide is evolved and the resulting radical is trapped by BrCCl3 to provide bromoarenes (3). Decarboxylative iodination is effected with iodoform or methylene iodide as the iodine donor. 

Decarboxylation of the silver salts of carboxylic acids in the presence of bromine or chlorine, the Hunsdiecker reaction, often is useful for the synthesis of alkyl halides ... 

Hunsdiecker reactions of salts of perfluoroalkanoic acids are known primarily as perhaps the best way of making perfluoroalkyl halides [58,306,307], but there have been other synthetic uses found for the perfluoroalkyl radicals which are formed by this decarboxylative process [308]. 

One great advantage of the decarboxylative halogenation with O-acyl esters of A-hydroxy-2-thiopyridone is that the reaction does not require any heavy metal such as Ag or Hg, unlike the Hunsdiecker reaction [24, 25]. Moreover, decarboxylative bromination of p-methoxybenzoic acid can be also carried out in good yield, while it does not proceed with the Hunsdiecker reaction instead, electrophilic bromination on the aromatic ring occurs. 

Needless to say, this was readily proven to be the case and a variety of chlorides, bromides and iodides have been prepared from the corresponding acids in good to excellent yields, by this method.14,15,26 31 In terms of mildness of conditions, generality and yields, this method is far superior to the classical Borodin-Hunsdiecker reaction and its variants.1011,26"31 As a demonstration of the mildness of the conditions, decarboxyl-ative bromination of the heavily functionalized acid 19 was carried out by Professor Ikegami to afford 20 (75 % yield), and... 

A variety of aromatic and vinylcarboxylic acids have also been decarboxylated an adaptations of this method involving the use of AIBN as chain initiator (equations 30 and 31). Unlike the classical Hunsdiecker reaction this variant is applicable to bodi election poor and electron rich aryl acids without the risk of electrophilic aromatic halogenation. 

Silver-mediated C—X bond formation was known for many years as the Hunsdiecker reaction, in which substrates bearing carboxylic acids are oxidatively decarboxylated to give alkyl halides in the presence of halogens (142). If olefins are used with silver benzoate and I2, the Prevost reaction occurs to yield diols (143). 

Another widely used series of reactions involves the addition of the hydrogen halides to alkenes. These are discussed in more detail later in the section on alkenes. Other methods that find some use include the decarboxylation of the dry silver salts of carboxylic acids by the halogens (the Hunsdiecker reaction). 

Hunsdiecker reaction of the silver salts of both cis-(56) and trans-2-methylcyclopropanecarboxylic acid (57) yielded the same mixture of cis- (58) and trans-1-bromo-2-methylcyclopropane (59), thus demonstrating that the 2-methylcyclopropyl radical was incapable of maintaining its configuration . Brominative decarboxylation of the silver salts of exo- (60) and em/o-norcarane-7-carboxylic acid (61) produced the same mixture (16 84) of exo- (62) and entio-7-bromonorcarane (63)". Similarly, cis- and trans-silver 1,2-cyclopropanedicarboxylate gave rise to the same isomer ratio (24 76) of cis- and fraws-1,2-dibromocyclopropane. Consistent with these results is the report that the Hunsdiecker reaction with the silver salt of trans-2,2,3-d3-cyclopropanecarboxylic acid (64) gives an equimolar mixture of cis- (65) and rrans-2,2,3-d3-cyclopropane (66) . 

This is a good method of synthesising symmetrical alkanes. The Kolbe reaction is usually performed using the potassium or sodium salt of the carboxylic acid. If the silver salt is reacted with bromine, then decarboxylation occurs again, but this time the alkyl bromide is formed. This reaction is called the Hunsdiecker reaction. The first step involves the formation of an acyl hypohalite, RC02X. 

The reduction of the derivatives which carboxylic acids form with the thiohydrox-amic acids (equation 15-48) provides a valuable alternative to the Hunsdiecker reaction for decarboxylating acids RCO2H to RH.107-15°-151... 

Thus illumination of a solution of the acid and the reagent provides a convenient method of decarboxylation comparable to the Hunsdiecker reaction, as in the example formulated ... 

Oxidative decarboxylation of optically active l-methyl-2,2-diphenylcyclopropanecarboxylic acid (10) with lead tetraacetate in the presence of iodine leads to racemized 1-iodo-l-methy 1-2,2-diphenylcyclopropane (11) in 45% yield. Subjecting 10 to the Cristol-Firth modification of the Hunsdiecker reaction (bromine and mercuric oxide in carbon tetrachloride) leads to racemic 1-bromo-l-methyl-2,2-diphenylcyclopropane (12) however, the yield is poor (5 /o). ... 

Finally, the ester group at C(4) provides a handle for further functionalization. It can be removed via a hydrolysis/decarboxylation sequence to provide the disubstituted thiazole nucleus [96]. On the other hand, hydrolysis of 188 was followed by a Hunsdiecker reaction to produce bromide 189. 

The preparation of chlorides by decarboxylation of carboxylic acids with lead tetraacetate and N-chlorosuccinimide as the chlorine donor in a 5 1 mixture of DM F and glacial acetic acid has been reported [71 a]. The reaction has been applied particularly often to the preparation of secondary and tertiary chlorides when the classic Hunsdiecker reaction gives low yields (Scheme 13.50) [71b]. This reaction proceeds by a radical pafhway. 

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