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Topic: reaction conditions  (Read 3607 times)

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Offline cvrlik

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reaction conditions
« on: November 16, 2012, 08:06:22 AM »
Hi!
Could anybody help with reaction conditions...
AlH3 is prepared in-situ from LiAlH4 and 1-bromopropane at room temperature. Then ester is added at room tempetature. The yield of the reaction is about 30%. I need to improve the result.
Thanks
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Offline Dan

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Re: reaction conditions
« Reply #1 on: November 16, 2012, 08:15:36 AM »
Do a literature search. This kind of reduction is widely reported to proceed in high yield with another very common reducing agent (Hint: also an aluminium hydride regent), I wouldn't be surprised if it has done before on that exact substrate in >80% yield.
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Offline zhangcarlin

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Re: reaction conditions
« Reply #2 on: November 16, 2012, 06:18:05 PM »
the classical reagent for the reduction of Conjugate ester to allylic alchol is  DIBAL. LAH is such a strong reangent that it is not easy to control.
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Offline OC pro

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Re: reaction conditions
« Reply #3 on: November 17, 2012, 12:32:48 PM »
Sodium borohydride should also do the job.
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Offline zhangcarlin

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Re: reaction conditions
« Reply #4 on: November 18, 2012, 05:34:26 AM »
Quote from: OC pro on November 17, 2012, 12:32:48 PM
Sodium borohydride should also do the job.
Do you have reference? I do not think Sodium borohydride works.
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Offline OC pro

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Re: reaction conditions
« Reply #5 on: November 18, 2012, 06:07:25 AM »
I have done reductions of esters with borohydride many many times. Simply dissolve your material in ethanol, add 1-1.5equiv. NaBH4 and let it stir for several hours (TLC control!).
OT: you can search databases on your own. I am not here to provide literature search, only experience. Just my two cents.
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Offline discodermolide

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Re: reaction conditions
« Reply #6 on: November 18, 2012, 06:18:19 AM »
I concur with OC pro. Sodium borohydride will reduce this ester.
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Offline zhangcarlin

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Re: reaction conditions
« Reply #7 on: November 18, 2012, 08:09:21 AM »
Quote from: OC pro on November 18, 2012, 06:07:25 AM
I have done reductions of esters with borohydride many many times. Simply dissolve your material in ethanol, add 1-1.5equiv. NaBH4 and let it stir for several hours (TLC control!).
OT: you can search databases on your own. I am not here to provide literature search, only experience. Just my two cents.

Sure, it is well-recoginzed that Sodium borohydride can reduce ester to primary alcohol. but my point is that have you seen any cases: it reduces conjugate ester to allylic alcohol?
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Offline Dan

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Re: reaction conditions
« Reply #8 on: November 18, 2012, 08:25:57 AM »
I would be worried about 1,4-reduction with sodium borohydride - however, this is from what I was taught, I haven't checked the literature in detail. Perhaps Luche conditions would minimise the problem.
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Offline orgopete

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Re: reaction conditions
« Reply #9 on: November 19, 2012, 02:31:45 AM »
What happens just with LiAlH4?
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Offline cvrlik

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Re: reaction conditions
« Reply #10 on: November 19, 2012, 03:23:02 AM »
Quote from: orgopete on November 19, 2012, 02:31:45 AM
What happens just with LiAlH4?
I am worried to use just LAH because reduction of carbon-carbon double bond could proceed... I guess...
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Offline orgopete

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Re: reaction conditions
« Reply #11 on: November 19, 2012, 10:30:31 AM »
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