Hunsdiecker-Cristol reaction

Hexyne, 159,231, 253 Homoconjugate addition, 219 Homogeranyl cyanide, 111, 112 Homologation, 272, 369 Horner-Wittig reaction, 61 Huang-Minlon reduction, 248 Hunsdiecker reaction, 279 Hunsdiecker-Cristol reaction, 323-324 Hydrazine, 26,248, 395 Hydrazine hydrate, 155, 336 Hydrazoic acid, 440... 

Hmtsdiecker Cristol reaction. (I, 657). A detailed procedure for the preparation of l-bromo-3-chlorocyclobutanc by the modified Hunsdiecker reaction has been published. A l-l. three-necked, round-bottomed flask wrapped with aluminum foil to exclude light and equipped with a mechanical stirrer, a reflux condenser, and an addition funnel, is charged with 37 g. (0.17 mole) of red mercuric oxide and 330 ml. 

In some cases we have combined similar reactions under one heading, for instance the Hunsdiecker-Borodin-Cristol-Firth decarboxy-iative bromination. It is not a simple task to decide whether credit is due to... 

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... 

Hunsdiecker reaction. The Cristol-Firth modification (1, 657 6,428) of this reaction generally proceeds in improved yield if irradiated with a 100-W bulb. ... 

Recently, Paquette and coworkers reported on the stereochemical consequences of having a trimethylsilyl substituent at the radical site. The Hunsdiecker reaction, as well as the Cristol-Firth modification thereof, on ( —)-(R)-l-trimethylsilyl-2,2-diphenyl-cyclopropanecarboxylic acid (71) resulted in racemic ( )-l-bromo-l-trimethylsilyl-2,2-diphenylcyclopropane (72). The trimethylsilyl group, bulky as it is, could not slow down the inversion frequency of the cyclopropyl a radical sufficiently to prevent complete racemization. More to the point, recentESR studies have demonstrated that the radical intermediate is planar, or nearly so. 

Tliis procedure, which is a modified Hunsdiecker reaction bused upon the method of Cristol and Firth, results in moderate 1(1 liigli yields of bromides and iodides from aliphatic and alicyclic carboxylic acuds, Carbon tc trachloride is most li cipiciiUy used as the solvent, but others can be einjiloycd. - ... 

The classical Hunsdiecker reaction was utilized in the laboratory of P.J. Chenier for the preparation of a highly strained cyclopropene, tricyclo[3.2.2.0 " ]non-2(4)-ene. The Diels-Alder cycloaddition was used to prepare the bicyclic 1,2-diacid, which surprisingly failed to undergo the Cristol-Firth modified Hunsdiecker reaction, most likely due to the unreactive nature of the diacid mercuric salt. However, the classical conditions proved to work better to afford the bicyclic 1,2-dibromide in modest yield. Treatment of this dibromide with f-BuLi generated the desired strained cyclopropene, which was trapped with diphenylisobenzofuran (DPIBF). 

Meyers, A. I., Fleming, M. P. Photoassisted Cristol-Firth-Hunsdiecker reaction. J. Org. Chem. 1979, 44, 3405-3406. 

Australian chemists4 report an instance where chlorodecarboxylation was effective where the Hunsdiecker reaction (Cristol-Firth modification) failed. Thus treatment of the acid (5) with lead tetraacetate in benzene in the presence of lithium chloride gave a... 

Hunsdiecker reaction. In the original Hunsdiecker reaction, the silver salt of an acid is prepared in one step and treated with bromine in another. Cristol found that isolation of a metal salt can be dispensed with addition of bromine to a refluxing snspension of red mercuric oxide in a solution of the acid in carbon tetrachloride affords the corresponding alkyl halide in good yield ... 

Davis et al. found the Cristol-Firth method most satisfactory for carrying out the Hunsdiecker reaction and suggest procedural details for improvement of results. 

Bromocyclopropane is also obtained from cyclopropanecarboxylic acid (3) in 41-46% yield by a Cristol-Firth modification of the Hunsdiecker reaction. ... 

The Cristol-Firth modification of the Hunsdiecker reaction applied to cis- and /ra 5-2-phenyl-cyclopropanecarboxylic acid (6) in tribromomethane leads to a mixture of cis- and trans-1-bromo-2-phenylcyclopropane (7) with predominant retention of configuration. "... 

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). ... 

In some cases we have combined similar reactions under one heading, for instance, the Hunsdiecker-Borodin-Cristol-Firth decarboxylative bromination. It is not a simple task to decide whether credit is due to the first discoverer of a reaction or to is developer. Often an improvement on a method is more useful than the original discovery, and usually one reaction owes its inception to some previous discovery non nova sed nove. 

In addition to Ag, many other metals (Hg, Pb, Tl, and Mn) can be used in the Hunsdiecker reaction.13-20 The Cristol-Firth modification is a one-pot reaction using excess red HgO and one equivalent of halogen.13 The advantage of the Cristol-Firth modification is that the mercury carboxylate does not need to be isolated and purified, unlike the Hunsdiecker reaction using the silver carboxylate. Therefore, as depicted by transformations 6— 714 and 8— 9,15 the Cristol-Firth modification is operationally more straightforward and more widely used than the classical Hunsdiecker reaction using silver carboxylate 1. 

Decarboxylation. Della and Patney recommend a two-step method for decarboxylation of bridgehead carboxylic acids. The first step is the Cristol-Firth modification of the Hunsdiecker reaction (I, 657, improved by use of methylene bromide as solvent). The second is photochemical reduction of the bromides by tri- -butyltin hydride (I, 1192-1193) with azobisisobutyronitrile as initiator. Yields are 80-95% in the first step and 80-90% in the second step. 

In the Hunsdiecker reaction, treatment of silver salts of carboxylic acids with bromine furnishes the alkyl(aryl) bromides with one less carbon atom. Improvements that do not require the preparation of the dry silver salts include the use of mer-cury(II) salts (Cristol-Firth modification) (eq 28), thallium(I) salts, and photostimulation. ... 

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