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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Mimic on July 11, 2018, 12:10:37 PM

Title: Horner-Wadsworth-Emmons vs Still-Gennari
Post by: Mimic on July 11, 2018, 12:10:37 PM

Both Horner-Wadsworth-Emmons and Still-Gennari reaction belongs to Wittig reaction. While Horner-Wadsworth-Emmons gives trans(E) olefine, Still-Gennari gives cis(Z) olefine. Starting posphonare is the same: what changes is the presence, in Still-Gennari reaction, of the 18-crown ether, who catch the base cation (e.g. Na⁺ from NaOH), so there is no formation of the six-term cycle, where the cation acts as a bridge between the two oxygen atoms

(https://i.imgur.com/h31sV04.gif)

(https://i.imgur.com/ug6H6Jw.gif)

In what way does the six-term cycle promote the trans(E) isomer formation?

Thanks in advance

Title: Re: Horner-Wadsworth-Emmons vs Still-Gennari
Post by: Babcock_Hall on July 11, 2018, 02:06:48 PM

What are your thoughts?

Title: Re: Horner-Wadsworth-Emmons vs Still-Gennari
Post by: Mimic on July 11, 2018, 04:18:03 PM

It could be in the formation of the phosphorus-oxygen bond (the one indicated with the trasversal arrow) make sure that R² group positions itself in an antiperiplanar manner with respect to the ester group