Mcmurry Reaction 3n5i3w

McMurry reaction From Wikipedia, the free encyclopedia

The McMurry reaction of benzophenone The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to an alkene using titanium chloridecompound such [1] chloride and a reducing agent. The reaction is named after its co-discoverer, J ohn E . McMurry. The McMurry reaction involved the use of a mixture TiC l3 and LiAlH 4, which produces the active reagent(s). Related species have been developed involving the combination of TiC l3 or TiC l4 with various other reducing agents, including potassium, zinc, and magnesium. [2][3] Contents [hide]    

1 Reaction mechanism 2 Background and scope 3 References 4 E xternal links [edit]Reaction mechanism This reductive coupling can be viewed as involving two steps. First is the formation of a pinacolate (1,2-diolate) complex, a step which is equivalent to the pinacol coupling reaction. The second step is the deoxygenation of the pinacolate which yields the alkene. The second step exploits the oxophilicity of titanium.

In this simplified cartoon, low-valent Ti transfers one electron each into each of two carbonyl bonds, followed by thedeoxygenation of resulting titanium diolato complex, yielding the alkene and titanium dioxide (for simplicity, depicted here as a molecule).

S everal mechanisms have been discussed for this reaction. [4] Low-valent titanium species induce coupling of the carbonyls by single electron transfer to the carbonyl groups. The required low-valent titanium species are generated via reduction, usually with zinc powder. This reaction is often performed in THF, which solubilizes intermediate complexes. The nature of low-valent titanium species formed is sensitive to conditions. [5] Bogdanovic and Bolte identified the nature and mode of action of the active species in some classical McMurry systems. [6] [edit]Background and scope The original publication by Mukaiyama demonstrated reductive coupling of ketones using reduced titanium reagents. [7] McMurry and Fleming coupled retinal to give carotene using a mixture of titanium trichloride and lithium aluminium hydride. O ther symmetrical alkenes were prepared similarly, e.g. civetone from adamantanone and tetraphenylethylene from benzophenone. A McMurry reaction usingtitanium tetrachloride and zinc is employed in the synthesis of a firstgeneration molecular motor. [8]

McMurry coupling to a molecular motor

In another example, the Nicolaou's total synthesis of Taxol uses this reaction, although coupling stops with the formation of a cis-diol, rather than an olefin. O ptimized procedures employ thedimethoxyethane complex of TiC l3 in combination with the Zn(C u). [edit]References 1. ^ J ohn E . McMurry, Michael P. Fleming (1974). method for the reductive coupling of carbonyls to olefins. S ynthesis of β-carotene". J. Am. Chem. Soc. 96 (14): 4708– 4709. doi:10.1021/ja00821a076. 4709. doi:10.1021/ja00821a076. 2. ^ Ian C . Richards “Titanium(IV) C hloride– Zinc” in E ncyclopedia of Reagents for O rganic S ynthesis, Wiley, London, 2001. doi:10.1002/047084289X.rt125. Article O nline O nline Posting Date: April 15, 2001 3. ^ Martin G . Banwell, “Titanium(III) C hloride– Lithium Aluminum Hydride” in E ncyclopedia of Reagents for O rganic S ynthesis J ohn Wiley, London, 2001. doi:10.1002/047084289X.rt129. Article O nline O nline Posting Date: April 15, 2001 4. ^ Michel E phritikhine (1998). "A new look at the McMurry reaction". Chem. Commun.: 2549– 2554.

5. ^ Borislav Alois Furstner, Borislav Bogdanovic (1996). "New developments in the chemistry of lowvalent titanium". Angew. Chem. Int. Ed. (35): 2442. 6. ^ Borislav Bogdanovic, Andreas Bolte (1995). "A comparative study of the McMurry reaction utilizing [HTiC l(THF) 0.5)]x, TiC l3(DME )1.5-Zn(C u) and as coupling reagents". J. Organomet. Chem. 502: 109– 121. doi:10.1016/0022-328X(95)05755-E . 7. ^ Mukaiyama, T.; S ato, T.; Hanna, “Reductive C oupling of C arbonyl C ompounds to Pinacols and O lefins by Using TiC l4 and Zn” C hem. Lett. 1973, 1041. doi:10.1246/cl.1973.1041 8. ^ Matthijs K. J . ter Wiel, Richard A. van Delden, Meetsma, and Ben L. Feringa (2003). "Increased S peed of Rotation for the S mallest Light-Driven Molecular Motor". J. Am. Chem. Soc. 125 (49): 15076– 15086. doi:10.1021/ja036782o. PMID 14653742.