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Topic: LiAlH4 + alpha-beta unsaturated ester  (Read 371 times)

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Offline xshadow

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LiAlH4 + alpha-beta unsaturated ester
« on: November 13, 2020, 10:42:50 AM »
Hi

I have a doubt...If I add LiAlH4 to a α-β unsaturated ester what will I get?

LiAlH4  +   -C=C-C=OOR


LiAlH4 will reduce only the C=O
Or will reduce before C=C and then C=O ?


I've seen an example with an unsaturated ketone and LiAlH4 has reduced only the C=O.
But here I have an ester and its C=O should be less reactive...so perhaps could happen that LiAlH4 attacks the C=C first.

So with an ester can LiAlH4  give 1,4 addition (and then 1,2 if in excess) ?? ....like RLi that gives 1,2 addition with aldehydes and ketones while 1,4 with ester and amide...??

THANKS!
« Last Edit: November 13, 2020, 11:25:37 AM by xshadow »

Offline rolnor

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Re: LiAlH4 + alpha-beta unsaturated ester
« Reply #1 on: November 13, 2020, 04:10:14 PM »
I think LAH is a very hard nucleophile and will attac the carbonyl much faster. I should ad that for beta-nitrostyrenes 1,4-addition is faster than reduction of the nitro group so maybe you will get a mixture?
« Last Edit: November 13, 2020, 04:46:19 PM by rolnor »

Offline xshadow

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Re: LiAlH4 + alpha-beta unsaturated ester
« Reply #2 on: November 13, 2020, 05:02:26 PM »
I think LAH is a very hard nucleophile and will attac the carbonyl much faster. I should ad that for beta-nitrostyrenes 1,4-addition is faster than reduction of the nitro group so maybe you will get a mixture?

Also RLi is a very hard nucleophile but attacks the C=O with 1,2 addition with aldehydes and ketones while for ester and amide it gives 1,4 addition (or at least a mixture) because the C=O of ester and amide is less reactive  towards a nucleohpilic attack

I wonder if  is it the same here...
I  haven't found much in the web, about the reaction of LiAlH4 with an unsaturated ester  (only found aldehydes and ketones examples)

Offline AWK

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AWK

Offline xshadow

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Re: LiAlH4 + alpha-beta unsaturated ester
« Reply #4 on: November 14, 2020, 03:38:39 AM »
https://pubs.acs.org/doi/10.1021/ja01187a511
thanks
seems it doesn't reduce C=C....

But in another site I've found the opposite...so strange
One other thing . in the last  step when they use K2Cr2O7 on an alcohol they only get an aldehyde....I've studied that K2Cr2O7 oxidizes primary alcohol to COOH.
For Aldehyde I should need something like PCC or swern...not Cr(vi)

Offline AWK

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Re: LiAlH4 + alpha-beta unsaturated ester
« Reply #5 on: November 14, 2020, 04:18:59 AM »
You have the opportunity to learn something new.
AWK

Offline rolnor

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Re: LiAlH4 + alpha-beta unsaturated ester
« Reply #6 on: November 14, 2020, 08:23:13 AM »
 Is not PCC Cr(vi)?

Offline xshadow

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Re: LiAlH4 + alpha-beta unsaturated ester
« Reply #7 on: November 15, 2020, 05:25:52 PM »
You have the opportunity to learn something new.

oook  ;D

Offline xshadow

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Re: LiAlH4 + alpha-beta unsaturated ester
« Reply #8 on: November 15, 2020, 05:26:26 PM »
Is not PCC Cr(vi)?
....right!
Sorry, I  mean K2Cr2O7  (the one used there)

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