Barton Decarboxylation

The Barton decarboxylation is a radical reaction named after its developer, the British chemist and Nobel laureate Sir Derek Barton. In this reaction, a carboxylic acid is converted to a thiohydroxamate ester, commonly referred to as a Barton ester. The product is then heated in the presence of a radical initiator and a suitable hydrogen donor, leading to a reductive decarboxylation. This process allows for the removal of carboxylic acid moieties from alkyl groups[1].

The reaction is initiated by the homolytic cleavage of a radical initiator, such as 2,2'-azobisisobutyronitrile (AIBN), upon heating. A hydrogen is then abstracted from the hydrogen source (for example, tributylstannane) to leave a radical. The N-O bond of the thiohydroxamate ester undergoes homolysis to form a carboxyl radical[1].

There have been advancements in the Barton decarboxylation process to circumvent some of its shortcomings, such as the use of toxic reductants, photochemical irradiation, unstable starting materials, and expensive catalysts. For instance, nickel-catalyzed decarboxylation has been developed, which is operationally simple and cost-effective. This method has been used for the decarboxylative fragmentation of redox-active NHPI esters[3].

Moreover, a red-light-mediated Barton decarboxylation has been described, which uses an energy transfer mechanism. This reaction is characterized by remarkably mild conditions, absence of hazardous materials, and low energy consumption[6][10].

Citations:

[1] https://en.wikipedia.org/wiki/Barton_decarboxylation

[2] https://www.sciencedirect.com/topics/chemistry/barton-decarboxylation

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5295468/

[4] https://www.wikiwand.com/en/Barton_decarboxylation

[5] https://www.youtube.com/watch?v=9eYiKABNcrw

[6] https://pubs.rsc.org/en/content/articlehtml/2023/sc/d3sc03643j

[7] https://en.wikipedia.org/wiki/Barton%E2%80%93McCombie_deoxygenation

[8] https://www.degruyter.com/document/doi/10.1515/9783110608373-012/html

[9] http://orgsyn.org/demo.aspx?prep=v89p0471

[10] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10583705/

[11] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Radical_Reactions_of_Carbohydrates_(Binkley)/Radical_Reactions_of_Carbohydrates_II:_Radical_Reactions_of_Carbohydrates/12:_Reactions_of_O-Thiocarbonyl_Compounds/II._Deoxygenation:_The_Barton-McCombie_Reaction

[12] https://www.lookchem.com/Chempedia/Basic-Chemical/Chemical-Reaction/8187.html

[13] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Synthesis_(Shea)/04:_Radical_Reactions