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The Markó–Lam deoxygenation is an organic chemistry reaction where the hydroxy 
This radical could be used for further chemical reactions or can abstract a hydrogen atom to form the deoxygenated product.
In presence of ketones, allylic derivatives lead to the coupling product when treated in Barbier's conditions with samarium diiodide.
functional group
In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
in an organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
is replaced by a hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
atom to give an alkyl group
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...
. The Markó-Lam reaction is a variant of the Bouveault–Blanc reduction and an alternative to the classical Barton–McCombie deoxygenation
The Barton–McCombie deoxygenation is an organic reaction in which a Hydroxyl, hydroxy functional group in an organic compound is replaced by a hydrogen to give an alkyl group. It is named after British chemists Sir Derek Harold Richard Barton an ...
. It is named for the Belgian chemists István Markó and Kevin Lam.
The main features of the reaction are:
*short reaction time (5 seconds to 5 minutes).
*the use of a stable toluate derivative.
*the use of SmI2/HMPA
Hexamethylphosphoramide, often abbreviated HMPA, is a phosphoramide (an amide of phosphoric acid) with the formula This colorless liquid is used as a solvent in organic synthesis.
Structure and reactivity
HMPA is the oxide of tris(dimethylamino ...
system or electrolysis instead of the classical and difficult to remove tributyltin hydride
Tributyltin hydride is an organotin compound with the formula (C4H9)3SnH. It is a colorless liquid that is soluble in organic solvents. The compound is used as a source of hydrogen atoms in organic synthesis.
Synthesis and characterization
The c ...
.
Mechanism
A hydroxyl group is first derivitised into a stable and very often crystalline toluate derivative. The aromatic ester is submitted to a monoelectronical reduction, by the use of SmI2/HMPA
Hexamethylphosphoramide, often abbreviated HMPA, is a phosphoramide (an amide of phosphoric acid) with the formula This colorless liquid is used as a solvent in organic synthesis.
Structure and reactivity
HMPA is the oxide of tris(dimethylamino ...
or by electrolysis, to yield the a radical-anion which decomposes into the corresponding carboxylate and into the radical of the alkyl fragment.
This radical could be used for further chemical reactions or can abstract a hydrogen atom to form the deoxygenated product.
Variations
In presence of methanol or isopropanol, the reduction lead to the selective deprotection of the aromatic esters.
In presence of ketones, allylic derivatives lead to the coupling product when treated in Barbier's conditions with samarium diiodide.
Scope
The Markó-Lam reaction was used as a final step in the total synthesis of Trifarienol B:
References
{{DEFAULTSORT:Marko-Lam Deoxygenation Free radical reactions Organic redox reactions Name reactions