the use of
SmI2/
HMPA system or electrolysis instead of the classical and difficult to remove
tributyltin hydride.
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[5] or by electrolysis,[6] 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.[7]
In presence of ketones, allylic derivatives lead to the coupling product when treated in Barbier's conditions with samarium diiodide.[8]
Scope
The Mark贸-Lam reaction was used as a final step in the total synthesis of Trifarienol B:[9]
^Lam, K.; Mark贸, I.E. (2009). "Chemoselective chemical and electrochemical deprotections of aromatic esters". Org. Lett.11 (13): 2752鈥2755.
doi:
10.1021/ol900828x.
PMID19492803.
^Takahashi, K.; Akao, R. & Honda, T. (2009). "Efficient diastereoselective synthesis of trifarane-type sesquiterpenes, trifarienols A and B". J. Org. Chem.74 (9): 3424鈥3429.
doi:
10.1021/jo900369t.
PMID19334700.