Kharash-Sosnovsky allylic oxidation

Today is the opening day of our new category, “Name reactions”. Here I’m going to write about well… name reactions. I don’t have any particular system how to choose the reactions but I’ll concentrate on reactions that are not so well-known. I think most of my readers (n=1? I know Milo was here) know so much about organic chemistry that featuring, for example, Diels-Alder reaction would be just pointless.

Today’s name reaction is known as Kharash-Sosnovsky allylic oxidation. It was originally described by Kharash and Sosnovsky in JACS in 1958 (DOI link). A more comprehensive study titled “The Copper-Catalyzed Reaction of Peresters with Hydrocarbons” was published 5 years later by Walling and Zavitsas in the same journal (DOI link). Below is one of the examples given by the gentlemen K and S themselves:

Kharash-Sosnovsky allylic oxidation

It might not be a “wow, that’s amazing!” kind of reaction, more like “hmm… interesting”, but quite nice considering that the selectivities are really good. For example, 1-hexene gives only hex-1-en-3-yl benzoate, and none of the isomeric hex-2-en-1-yl benzoate.

Selectivity of Kharash-Sosnovsky allylic oxidation

“How does that work?!”, I hear the audience scream. Well, below is how the authors of the latter article say it works. They have another option also for the last two steps, where the radical R directly reacts with the benzoate anion.

Kharash-Sosnovsky allylic oxidation mechanism

That’s it for today. Feel free to comment.

edit: I replaced the links to .pdfs with DOIs. Thanks to Mitch from Chemical Forums for suggesting that.

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8 Comments on “Kharash-Sosnovsky allylic oxidation”

  1. Mitch Says:

    Please use DOIs when linking to a paper. We need a standard for this type of communication and it exists as DOIs. So the first .pdf’s url would be http://dx.doi.org/10.1021/ja01536a062

    I know its easier to put a link to the article’s pdf. But, I’ve seen publishers change their url structures, so they are not permanent markers to the article, but DOIs are. Some publisher’s url are sessid dependent, so it will only work for your computer’s cache, ACS doesn’t do this, but just an example on why you shouldn’t use hard .pdf urls.

    Mitch

  2. yepyep Says:

    Sure. I’ll change them later today.

    And thanks for the tip, I appreciate it. See, I’m still a blogging newbie. :)

  3. Felix Says:

    Why does the allylic radical/cation only react in 3 position and not in 1?

  4. Mitch Says:

    Secondary radicals are more stable than primary radicals. Also, allylic radicals are more stable than vinyllic radicals.

  5. Uncle Al Says:

    The harder the Lewis base solvent (e.g., water) the more Cu(II) is stabilized. The softer the Lewis base solvent (e.g., MeCN), the more Cu(I) is stabilized. One could diddle with Cu(I)Cu(II) redox potential. PhCN if volatility is a bother.

  6. milkshake Says:

    If you read the second paper closely, you will find that the result is less clear-cut than advertised in the first paper – that with alpha olefins the ratio of produced allylic esters is about 85:15 (1-alkene-3-yl vs 2-alkene-1-yl). The first paper came from period when people did not have NMRs so missing 15% of an isomer was easy.

  7. atompusher Says:

    Heterogeneous CuBr surface chemistry… eecch. I bet a rusty nail would catalyze this reaction…

  8. Rahman M T Says:

    In the mechanistic part, 3rd equation, Cu(II) should be reduced to Cu(I).


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