Decarboxylative bromination

Kinetic studies of the oxidation of aspirin by bromamine-T, A-bromosuccinimide (NBS), and A-bromophthalimide (NBP) support a mechanism in which the unpro-tonated oxidant is the active species. " The ultimate product of the reaction is 2,4,6-tribromophenol, which arises through decarboxylation, bromination and loss of acetic acid. The NBP and NBS oxidations of -hydroxy acids are found to be similar in mechanism. 

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. 

Vogel and coworkers have described the synthesis of anti-1,6 7,12-/ wmethano[ 14]annulene 44 for studies of its -electron structure.32 Incorporation of AIBN into decarboxylative bromination of vinylogous carboxylic acid 45 via Barton esters increased the efficiency of this reaction, Scheme 16b. Harvey... 

Perhaloalkanes serve as bromination or iodination agents in the radical decarbox-ylative halogenation of carboxylic acids. In an interesting modification of the Hunsdiecker-Bodin reaction Barton and coworkers have applied iV-hydroxypyridine-2-thione esters as nonelectrophilic intermediates for the decarboxylative bromination and iodination of primary, secondary and tertiary aliphatic and alicyclic592, as well as aroma-... 

HUNSDIECKER - BORODIN CRISTOL - FIRTH Decarboxylation - Bromination... 

Barton, D. H. R., Lacher, B., Zard, S. Z. The invention of radical reactions. Part XVI. Radical decarboxylative bromination and iodination of aromatic acids. Tetrahedron 1987, 43, 4321-4328. 

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. 

Similar to IBX, the synthetic utility of DMP goes beyond the standard selective oxidation of primary and secondary alcohols. A simple and mild method of decarboxylative bromination of a,p-unsaturated carboxylic acids has been developed using DMP in combination with tetraethylammonium bromide (TEAB) at room temperature.22 It was observed that electron donating groups attached to the phenyl ring of the a,P-unsaturated carboxylic acids undergo fast decarboxylation/bromination in excellent yields (48 — 49). 

Electron withdrawing groups attached to the phenyl ring of a,P-unsaturated carboxylic acids undergo slow decarboxylation/bromination in moderate yields (SO — 51). 

Aliphatic groups next to a,p-unsaturated carboxylic acid moiety also undergo fast decarboxylation/bromination in good yields (52 — 53). 

Hunsdiecker reaction. Decarboxylative bromination is achieved photochemically by this reagent combination. 

The oxidation of aspirin by A-sodio-A-bromobenzenesulfonamide (bromamine-B, BAB) in aqueous HCIO4 is first order in BAB, fractional order in aspirin and inverse fractional order in H+. The reaction proceeds via decarboxylation, bromination, and AcOH loss, affording the product 2,4,6-Br3CeH20H. The oxidation of D-cycloserine (CS) by BAB in HCl is first order in BAB and fractional order each in CS and H+. The proposed mechanism assumes simultaneous catalysis by H+ and Cl ions and is consistent with the observed kinetic results. The oxidation of diethylamine by BAB catalysed by ruthenium(III) is first order in oxidant, catalyst and substrate, but inverse fractional order in H+. A mechanism in which the metal coordinates the nitrogen atom of the amine before a slow electrophilic attack on the nitrogen by BAB, elimination of HBr, attack by water, and disproportionation affords acetaldehyde and ethylamine, which undergoes a similar oxidation. " ... 

Decarboxylative bromination Dipyrromethenes from dipyrromcthancs Preferential debenzylation of carboxylic acid esters... 

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