Barton-McCombie deoxygenation
| Barton–McCombie deoxygenation | |
|---|---|
| Named after |
Derek Harold Richard Barton Stuart W. McCombie |
| Reaction type | Organic redox reaction |
| Identifiers | |
| Organic Chemistry Portal | barton-mccombie-reaction |
| RSC ontology ID | RXNO:0000134 |
The Barton–McCombie deoxygenation is an organic reaction in which an hydroxy functional group in an organic compound is replaced by a hydrogen to give an alkyl group. 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. The alcohol (1) is first converted into a reactive carbonothioyl intermediate such as a thionoester or xanthate (2). Then, tributylstannane 3 is decomposed by AIBN 8 into a tributylstannyl 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 tributylstannane generating the desired deoxygenated product (6) and a new radical species ready for propagation.
The main disadvantage of this reaction is the use of tributylstannane which is toxic, expensive and difficult to remove from the reaction mixture. One alternative is the use of tributyltin oxide as the radical source and poly(methylhydridesiloxane) (PMHS) as the hydrogen source. Phenyl chlorothionoformate used as the starting material ultimately generates carbonyl sulfide.
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