Barton-McCombie deoxygenation

The Barton-McCombie deoxygenation is an organic reaction in which an hydroxy functional group in an organic compound is replaced by a hydride to give an alkyl group [cite journal
author = Barton, D. H. R.; McCombie, S. W.
journal = J. Chem. Soc., Perkin Trans. 1
title = A new method for the deoxygenation of secondary alcohols
year = 1975
volume = 16
pages = 1574–1585
doi = 10.1039/P19750001574
] [cite journal
author = Crich, D.; Quintero, L.
journal = Chem. Rev.
title = Radical chemistry associated with the thiocarbonyl group
year = 1989
volume = 89
pages = 1413–1432
doi = 10.1021/cr00097a001
] . It is named for the British chemists Sir Derek Harold Richard Barton (1918–1998) and Stuart W. McCombie.

This deoxygenation reaction is a radical substitution. In the related Barton decarboxylation the reactant is a carboxylic acid.


The reaction mechanism consists of a catalytic radical initiation step and a propagation step. [Forbes, J. E.; Zard, S. Z. "Tetrahedron Lett." 1989, "30", 4367.] The alcohol (1) is first converted into a xanthate (2). The other reactant tributyltin hydride 3 is decomposed by AIBN 8 into a tributyltin radical 4. The tributyltin radical abstracts the xanthate group from 2 leaving an alkyl radical 5 and tributyltin xanthate (7). The sulfur tin bond in this compound is very stable and provides the driving force for this reaction. The alkyl radical in turn abstracts a hydrogen atom from a new molecule of tributyltin hydride generating the desired deoxygenated product (6) and a new radical species ready for propagation.


Alternative hydride sources

Main disadvantage of this reaction is the use of the tin hydride which is toxic, expensive and difficult to remove from the reaction mixture. One alternative is the use of tributyltin anhydride as the radical source and poly(methylhydridesiloxane) (PMHS) as the hydride source [α-D-Ribo-hexofuranose, 3-deoxy-1,2:5,6-bis-O-(1-methylethylidene). Tormo, J.; Fu, G. C. "Org. Syn.", Coll. Vol. 10, p.240 (2004); Vol. 78, p.239 (2002). ( [ Article] )] . Phenyl chlorothionoformate used as the starting material ultimately generates carbonyl sulfide.

Trialkyl boranes

An even more convenient hydrogen donor is provided by trialkylborane-water complexes ["Deoxygenation of Alcohols Employing Water as the Hydrogen Atom Source" David A. Spiegel, Kenneth B. Wiberg, Laura N. Schacherer, Matthew R. Medeiros, and John L. Wood "J. Am. Chem. Soc." 2005, "127", 12513-12515. (DOI|10.1021/ja052185l)] such as trimethylborane contaminated with small amounts of water.

In this catalytic cycle the reaction is initiated by air oxidation of the trialkylborane 3 by air to the methyl radical 4. This radical reacts with the xanthate 2 to S-methyl-S-methyl dithiocarbonate 7 and the radical intermediate 5. The CH3B.H2O complex 3 provides a hydrogen for recombining with this radical to the alkane 6 leaving behind diethyl borinic acid and a new methyl radical.

It is found by theoretical calculations that that a O-H homolysis reaction in the borane-water complex is endothermic with an energy similar to that of the homolysis reaction in tributyltin hydride but much lower than the homolysis reaction of pure water.


A variation of this reaction was used as one of the steps in the total synthesis of azadirachtin ["Synthesis of Azadirachtin: A Long but Successful Journey" Gemma E. Veitch, Edith Beckmann, Brenda J. Burke, Alistair Boyer, Sarah L. Maslen, and Steven V. Ley Angew. Chem. Int. Ed. 2007, DOI|DOI: 10.1002/anie.200703027] :


In another variation the reagent is the imidazole 1,1'-thiocarbonyldiimidazole (TCDI), for example in the total synthesis of pallescensin B. ["The first total synthesis of (±)-pallescensin B" Wen-Cheng Liu and Chun-Chen Liao Chem. Commun., 1999, 117–118 117 [ Article] ] . TCDI is especially good to primary alcohols because there is no resonance stabilization of the xanthate because the nitrogen lonepair is involved in the aromatic sextet.


The reaction also applies to S-alkylxanthates. With triethylborane as a novel metal-free reagent, the required hydrogen atoms are abstracted from protic solvents, the reactor wall or even (in strictly anhydrous conditions) the borane itself. ["Part 2. Mechanistic aspects of the reduction of S-alkyl-thionocarbonates in the presence of triethylborane and air" Allais F, Boivin J, Nguyen V Beilstein Journal of Organic Chemistry, 2007 3:45 ( 12 December 2007 ) doi|10.1186/1860-5397-3-46]


External links

* [ Barton-McCombie @]
* Chemical & Engineering News [ article on alkylborane reaction]

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Barton-McCombie-Desoxygenierung — Die Barton Desoxygenierung (korrekt: Barton McCombie Desoxygenierung) ist eine Namensreaktion der organischen Chemie und ist nach den britischen Chemikern Sir Derek Harold Richard Barton and Stuart W. McCombie benannt. Sie beschreibt eine… …   Deutsch Wikipedia

  • Deoxygenation — is a chemical reaction involving the removal of molecular oxygen (O2) from a reaction mixture or solvent, or the removal of oxygen atoms from a molecule. Classic representatives of deoxygenation are: the replacement of a hydroxyl group by… …   Wikipedia

  • McCombie — may refer to: Andy McCombie (1876–1952), a Scottish international footballer Karen McCombie (born 1963), an author of children and young adult novels William McCombie (1805–1880), Scottish agriculturist famed for a herd of black polled cattle See …   Wikipedia

  • Barton-Desoxygenierung — Die Barton Desoxygenierung (korrekt: Barton McCombie Desoxygenierung) ist eine Namensreaktion der Organischen Chemie und nach den britischen Chemikern Derek Harold Richard Barton und Stuart W. McCombie benannt. Sie beschreibt eine zweistufige… …   Deutsch Wikipedia

  • Derek Barton — Sir Derek Barton Born 8 September 1918(1918 09 08) Gravesend, England Died 16 March 1998(1998 03 16) …   Wikipedia

  • Markó–Lam deoxygenation — The Markó–Lam deoxygenation is an organic chemistry reaction where the hydroxy functional group in an organic compound is replaced by a hydrogen atom to give an alkyl group.[1][2] The Markó Lam reaction is a variant of the Bouveault–Blanc… …   Wikipedia

  • Réaction de Barton-Motherwell — La réaction de Barton Motherwell (ou décarboxylation de Barton Motherwell) est une séquence réactionnelle permettant d effectuer sélectivement une réduction d un acide carboxylique en alcane. Elle fut mise au point par Sir Derek Harold Richard… …   Wikipédia en Français

  • Alkane — Not to be confused with Alkene or Alkyne. Chemical structure of methane, the simplest alkane Alkanes (also known as paraffins or saturated hydrocarbons) are chemical compounds that consist only of hydrogen and carbon atoms and are bonded… …   Wikipedia

  • Alcano — El metano es el primer alcano. Los alcanos son hidrocarburos, es decir que tienen solo átomos de carbono e hidrógeno. La fórmula general para alcanos alifáticos (de cadena lineal) es CnH2n+2, y para cicloalcanos es CnH2n. También reciben el… …   Wikipedia Español

  • Physical Sciences — ▪ 2009 Introduction Scientists discovered a new family of superconducting materials and obtained unique images of individual hydrogen atoms and of a multiple exoplanet system. Europe completed the Large Hadron Collider, and China and India took… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.