The Markó–Lam deoxygenation is an organic chemistry reaction where the hydroxy

Hydroxyl

A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...

 functional group

Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

 in an organic compound

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 is replaced by a hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 atom to give an alkyl group

Alkane

Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...

. The Markó-Lam reaction is a variant of the Bouveault–Blanc reduction and an alternative to the classical Barton–McCombie deoxygenation. It is named for the Belgian chemists Istvan Marko and Kevin Lam.

The main features of the reaction are :

• its short reaction time (between 5 seconds to 5 minutes).
• the use of a stable toluate derivative.
• the use of SmI₂/HMPA system or electrolysis instead of the classical and difficult to remove tributyltin hydride
  Tributyltin hydride
  Tributyltin hydride is an organotin compound with the formula 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:...
  
  .

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 or by electrolysis, to yield the a radical-anion which decomposes into the corresponding carboxylate and into the radical of the alkyl part.
This radical could be used for further chemical reactions or can abstract an 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: