Alcohols carbon atom deoxygenation

Reaction of Carbon Atoms with Alcohols and Ethers. The electro-philicity of atomic carbon and the exothermicity of carbon monoxide formation in its reactions facilitates attack on, and removal of oxygen by C atoms. Deoxygenation of ethers, alcohols, and carbonyl compounds has been reported. This process is generally a highly exothermic reaction, which is likely to generate products with excess energy. 

Scheme 5.9 illustrates some of the conditions that have been developed for the reductive deoxygenation of alcohols. Entries 1 to 4 illustrate the most commonly used methods for generation of thiono esters and their reduction by tri-M-butylstannane. These include formation of thiono carbonates (Entry 1), xanthates (Entry 2), and thiono imidazolides (Entries 3 and 4). Entry 5 is an example of use of dimethyl phosphite as the hydrogen donor. Entry 6 uses r .s-(trimethylsilyl)silane as the hydrogen atom donor. 

Eq. 3.7 shows the cyclization of the xanthate ester (20) formed from homopropargyl alcohol, through 5-exo-dig manner of the formed carbon-centered radical. This reaction is not a deoxygenation reaction of alcohol, but the cyclization of the carbon-centered radical formed from the addition of Bu3Sn to the thiocarbonyl-sulfur atom, onto the side-chained triple bond to form thionolactone, the hydrolysis of which readily creates lactone (21) [21-23]. 

Finally, we note that interception of the carbon radical by a proximate C=C or C C system, which has received much attention in recent years as a useful synthetic tool, can be a problem when simple deoxygenation is desired at a center five or six atoms removed from the multiple bond. The efficient, planned cyclization of (90) to (91) also represents an unsuccessful deoxygenation of a secondary alcohol The initial adduct radicals (to C=S) have also been trapped in intramolecular reactions. ... 

Deoxygenation. Alkanes are obtained from alcohols by reaction with PdClj-EtjSiH (by adding an alkyl halide such as Mel to the reaction medium the halides are produced). Secondary allylic alcohols and acetates are reduced to the hydrocarbons with EtjSiH-LiClO. The facile removal of the oxygen atom from aryl ketones by TiCl -mediated reaction with Et,SiH makes the synthesis of a-amino acids containing carbon chains of different length and a terminal aryl group much easier. A synthesis of CHIRAPHOS via the phosphine oxides calls for deoxygenation with HSiCl -EtaN." ... 

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