Eddygp
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Posts: 858
Registered: 31-3-2012
Location: University of York, UK
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Mood: Organometallic
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Preparation of (3Z)-4-phenylbut-3-en-2-ol
Or, as a trivial name, cis-benzylideneacetone.
It is widely known that a simple aldol condensation between acetone and benzaldehyde will yield 4-phenylbut-3-en-2-one, which would easily be reduced
to form the alcohol.
However, a very significant part will go all the way to dibenzylideneacetone and, furthermore, the vast majority of the benzylideneacetone formed is,
in fact, the trans (E) isomer.
To overcome this, I have thought about reacting sodium phenylacetylide (synthesis here) with acetaldehyde (if not readily available, prepare by reacting ethanol with PCC).
The resulting compound, 4-phenyleth-3-yn-2-ol can be reduced with Lindlar catalyst to form (3Z)-4-phenyleth-3-en-2-ol, which unfortunately comes out
as a racemate.
Oxidation of this alcohol would yield the cis-enone, probably useful if Diels-Alder like reactions are desired or Michael addition ones.
The good aspect is that it is easily made from fairly OTC reagents*, as well as providing a nice ground to prepare more exciting compounds (the enone
is a great dienophile, but apart from Diels-Alder, many other syntheses can be attempted).
* As long as you can get some Lindlar, I guess.
there may be bugs in gfind
[ˌɛdidʒiˈpiː] IPA pronunciation for my Username |
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CuReUS
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Registered: 9-9-2014
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| Quote: | | However, a very significant part will go all the way to dibenzylideneacetone |
what if the benzaldehyde was slowly dripped into a flask with an excess of acetone ? I have read somewhere that there is a trick to control these type
of reactions.Instead of using benzaldehyde directly,convert it into its bisulphite salt and then use it.
if you wanted the enone,why didn't you react phenylacetylene with ethyl acetate itself ?
http://onlinelibrary.wiley.com/doi/10.1002/anie.200802162/fu...
I had two other ideas to get the cis-enone
1. why don't you react benzaldehyde with the lithium enolate(using LDA) or silyl enol ether of acetone(mukaiyama aldol addition) to get the
b-hydroxyketone.Then you could use a special dehydrating agent(don't ask me what) which will dehydrate to give only the cis-enone
2.or you could make (3Z)-4-phenylbut-3-ene and then oxidise the 2 position to ketone directly
http://www.sciencedirect.com/science/article/pii/S0040402001...
also a paper on converting E to Z using photocatalysts
http://pubs.acs.org/doi/abs/10.1021/ja5019749
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