Chemists from Switzerland and Japan have developed a cross-coupling reaction of organosodium compounds with alkyl halides. First, they learned to obtain dimerization products of organosodium compounds in the presence of an iron catalyst, and then optimized the cross-coupling reaction. The study was published in Nature Synthesis.
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Organosodium compounds are rarely used. This is because they are very reactive, making them difficult to obtain and store. In addition, they are poorly soluble in non-polar solvents, and are simply unstable in coordinating solvents.
However, as early as the 19th century, chemists Charles Adolphe Wurtz and Wilhelm Rudolf Fittig discovered several reactions of coupling aryl halides and alkyl halides in the presence of excess metallic sodium. These reactions are not used today because they are not selective and work only for specially selected substrates.
However, chemists led by Eva Hevia from the University of Bern and Sobi Asako from the RIKEN Institute for Physical Chemistry and Nuclear Research have now learned to use organosodium compounds to carry out catalytic cross-coupling.
To find out whether such a reaction could occur, the chemists took a pre-prepared aryl sodium derivative and mixed it with iron acetylacetonate in the presence of di-tert-butyl peroxide. It turned out that under these conditions, the aryl sodium compound dimerizes to form biaryl. Thus, the scientists found out that the iron complex can catalyze the homocoupling of organosodium compounds.
The scientists then tried a cross-coupling reaction. They mixed the same aryl sodium derivative, iron complex, and cyclohexyl bromide with the idea of getting a product of a combination of the aryl and cyclohexyl fragments. But instead, a dimerization product was formed again.
To overcome this problem, the chemists carried out several reactions in the presence of different coordinating additives capable of reacting with the organosodium derivative and changing its reactivity. It turned out that the cross-coupling product was formed with a yield of 41 percent in the presence of tetramethylethylenediamine. And by additionally selecting the conditions, the scientists achieved a yield of 82 percent.
Thus, chemists showed that the long-discovered Wurtz-Fittig reaction could be carried out in a catalytic version without using excess metallic sodium. Moreover, both primary and secondary alkyl bromides entered into it, and protected alcohol groups and tertiary amino groups in the reagents did not interfere with its course.
We recently reported on how an iron complex catalyzed the Suzuki reaction.