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Author Topic: Horner-Wadsworth-Emmons vs Still-Gennari  (Read 500 times)

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Mimic

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Horner-Wadsworth-Emmons vs Still-Gennari
« on: July 11, 2018, 06:10:37 AM »

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





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

Thanks in advance
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Babcock_Hall

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Re: Horner-Wadsworth-Emmons vs Still-Gennari
« Reply #1 on: July 11, 2018, 08:06:48 AM »

What are your thoughts?
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Mimic

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Re: Horner-Wadsworth-Emmons vs Still-Gennari
« Reply #2 on: July 11, 2018, 10:18:03 AM »

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
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