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.{{cite web|url=https://www.organic-chemistry.org/synthesis/C1H/deoxygenations.shtm |title=Alkane synthesis by deoxygenation |publisher=Organic-chemistry.org|accessdate=2010-01-01}}[http://www.chem-station.com/odos/2010/06/-marko-lam-deoxygenation.html マルコ・ラム脱酸素化 Marko-Lam Deoxygenation – ODOOS -合成反応データベース- by Chem-Station]. Chem-station.com (2010-06-06). Retrieved on 2014-01-28. The Markó-Lam reaction is a variant of the Bouveault–Blanc reduction{{cite journal|last1 = Bouveault|first1 = L.|authorlink1=Louis Bouveault|last2 = Blanc|first2 = G. L.|journal = Bull. Soc. Chim. Fr.|year = 1904|volume = 31|pages = 666–672|title = Transformation des acides monobasiques saturés dans les alcools primaires correspondants|language = French|trans-title = Transforming saturated monobasic acids into the corresponding primary alcohols|url = http://gallica.bnf.fr/ark:/12148/bpt6k5469971k/f670.image}} and an alternative to the classical Barton–McCombie deoxygenation. It is named for the Belgian chemists István Markó and Kevin Lam.{{cite web |url=http://www.lamresearchgroup.com/ |title=Home |website=lamresearchgroup.com}}
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 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{{cite journal|author1=Lam, K. |author2=Markó, I.E. |journal= Org. Lett.|year= 2008|volume= 10|issue=13|pages= 2773–2776|doi=10.1021/ol800944p|pmid=18507394|title=Using toluates as simple and versatile radical precursors}} or by electrolysis,{{cite journal|author1=Lam, K. |author2=Markó, I.E. |journal=Chem. Commun. |year=2009 |volume=2009 |issue=1 |pages=95–97 |doi=10.1039/b813545b |pmid=19082010 |title=Organic electrosynthesis using toluates as simple and versatile radical precursors|url=http://gala.gre.ac.uk/id/eprint/21432/3/21432%20LAM_Organic_Electrosynthesis_Using_Toluates_2008.pdf }} 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.{{cite journal|author1= Lam, K.|author2= Markó, I.E.|journal= Org. Lett.|year= 2009|volume= 11|issue= 13|pages= 2752–2755|doi= 10.1021/ol900828x|pmid=19492803|title= Chemoselective chemical and electrochemical deprotections of aromatic esters}}
File:MarkoLam_Hydrolysis_colored.svg
In presence of ketones, allylic derivatives lead to the coupling product when treated in Barbier's conditions with samarium diiodide.{{cite journal|author1=Lam, K. |author2=Markó, I.E. |journal=Tetrahedron |year=2009 |volume=65 |issue=52|pages=10930–10940 |doi=10.1016/j.tet.2009.09.111 |title=Toluates: Unexpectedly versatile reagents}}
Scope
The Markó-Lam reaction was used as a final step in the total synthesis of Trifarienol B:{{cite journal|author1=Takahashi, K. |author2=Akao, R. |author3=Honda, T. |name-list-style=amp |journal=J. Org. Chem. |year=2009 |volume=74 |issue=9|pages=3424–3429 |doi=10.1021/jo900369t |pmid=19334700 |title=Efficient diastereoselective synthesis of trifarane-type sesquiterpenes, trifarienols A and B }}
References
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Category:Free radical reactions