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Topic: Lithium acetylide + amide with a conjugated double bond?  (Read 4484 times)

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Offline kims

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Lithium acetylide + amide with a conjugated double bond?
« on: April 15, 2008, 11:50:45 PM »
the lithium acetylide doesn't attack the carbonyl apparently so do its do conjugate addition?
help please


Offline venkatjohnny

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Re: Lithium acetylide + amide with a conjugated double bond?
« Reply #1 on: April 16, 2008, 04:37:04 AM »
Hi,
lithium acetylide is a hard nucleophile , so it attacks mainly on hard electrophile like carbonyl centre(hard-hard interactions). To attack on alkene carbon u need to have a soft nucleophile. For example Gilman reagent is a soft nucleophile( R2CuLi), Cu makes the R group to be soft. That's why all the Gilman reagents will result in conjugate addition.
Better u refer ORGANIC CHEMISTRY by CLAYDEN for this orbital interaction topic..have a nice time

Offline kims

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Re: Lithium acetylide + amide with a conjugated double bond?
« Reply #2 on: April 16, 2008, 01:15:56 PM »
i did the hard to hard in the carbonyl carbon but apparently this is the wrong product. so i was wondering what other possibilities there were. thanks

Offline sjb

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Re: Lithium acetylide + amide with a conjugated double bond?
« Reply #3 on: April 16, 2008, 01:30:30 PM »
As I mentioned previously, I think Weinreb amides (the RNMeOMe species) react with organolithiums to form ketones.

So, after forming the alcohol (or more probably the alkoxide in this case, as I don't see any acid in your conditions), I think the tetrahedral intermediate collapses and kicks out -NMeOMe.

Initial product perhaps the keto-acetylene? I'm not sure how labile TMS is in your system, this may fall off?

S

Offline kims

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Re: Lithium acetylide + amide with a conjugated double bond?
« Reply #4 on: April 16, 2008, 06:10:05 PM »
Is this what you are talking about?


Offline macman104

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Re: Lithium acetylide + amide with a conjugated double bond?
« Reply #5 on: April 16, 2008, 07:49:08 PM »
Yes, that is what is meant.  Check this link for more info.

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