Archive for the ‘Name reactions’ category

Kharash-Sosnovsky allylic oxidation

December 12, 2006

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.