Pixel
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Would this reduction work?
I have been working on a reduction of bromo substituted tryptamines derivatives for a while. Would the amide group course any trouble? Could NaBH4 do
the job without lowering the yeild to much?
I attached the reaktion as a GIF image, hope it will work.
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Pixel
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Well the attachment did'nt work so here is the full names:
2-(2-bromo-1H-indol-3-yl)-N-isopropylacetamide --------> 2-(1H-indol-3-yl)-N-isopropylacetamide
Would NaBH4 do the job without getting to many side reaktions?
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Nicodem
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No, NaBH4 by itself would not do the job.
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chemrox
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would LAH do the wanted reduction?
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Nicodem
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LiAlH4 reduces amides to amines.
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Pixel
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I read something about a reduction with nBu-Li in THF. I don't know if this reducing agent would couse the same trouble as LiAlH4.
Isnt there a easyer way to dehalogenate?
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Nicodem
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| Quote: | Originally posted by Pixel
I read something about a reduction with nBu-Li in THF. I don't know if this reducing agent would couse the same trouble as LiAlH4.
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BuLi is not an actual reducent but it can swap the bromine in ArBr with lithium atom thus forming ArLi which yieds ArH upon quenching with an acid
like H2O or similar. It is however an extremely strong base (estimated pKa for butane is 45!) and it will thus deprotonate just about anything it can
(indole NH, amide NH, the amide alpha H, hydrogens on positions near coordinative groups...) and thus at least a quadruple excess needs to be used
(since another equivalent is lost by the reaction of the side product BuBr with BuLi yielding butane, butene and LiBr). But since BuLi is also a very
strong C-nucleophile (just like Grignard reagents) it is useless for your substrate that has the weakly so but nevertheless electrophilic carbonyl.
| Quote: | | Isnt there a easyer way to dehalogenate? |
You could have asked that in the first post and I would have told you that the only practical method to exchange that Br with H is by hydrogenation
with 5% Pd on carbon (use at least 5 mol%) and with 1 eq of Et3N as HBr scavenger. 5-10h at >40 PSI should suffice, but follow the pressure drop
and check with TLC before workup.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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