Flip
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Hydroboration
I queried "hydroboration" and "BH3" on the search engine to discover that there is precious little on the reaction, actually next to nothing,
availiable here on the forum. We must rectify this problem.
A little bit of background on the reaction... it is an electrophilic, anti-markovnikov addition of BH3 or HB-R2 to an alkene or alkyne, generally
yeilding an alcohol or an enol. Most experts believe that it is a one-step concerted addition with a cyclic transition state. It can be run at room
temperature or with heating and generally the reagent for hydroboration is an organoborane complex of BH3 and THF.
Another plus of the reaction is the stoichiometry, as BH3 will often add to three different molecules simultaneously before the oxidation and
replacement with -OH. Quite an elegant reaction, if you ask me.
So my interest then is two-fold - first, does anyone have any experience with the reaction or stories to relate on the subject of hydroboration? No
one on this forum has of yet reported actually performing this reaction. Can anyone share some more insight into the reaction and it's optimal
conditions? Can anyone dig up any practical, procedural references on the hydroboration of alkenes or alkynes?
Second, I would very much like to know if some other organoborane complex might be used (efficiently) instead of BH3-THF. Is there any way
(preferably OTC) that a proper organoborane can be formed... as a substitute for THF would be extremely helpful to me.
So this is the hydroboration thread, and I hope that anyone here capable will contribute, as I feel it would be a great addition to the forum and may
open a great number of synthetic possibilities.
Thanks,
Flip
[Edited on 6-3-2006 by Flip]
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DDTea
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Actually, this reaction is one of the first we were taught in my organic chemistry class. It was taught for, as you said, adding to double bonds in
an Anti-Markovnikov manner.
As a strange side note, the way I remembered this reaction was by saying Markovnikov, a great Russian scientist, was in fact a communist. Why? Look
at his philosophy, imagining an addition of HBr to (CH3)2C=CH2 . The little CH2 will only get the small Hydrogen, while the substituted Carbon gets
the big Bromine! He who has more will always get more, while he who has less always gets less. Sounds like the rant of a Communist, no??
But Hydroboration to the rescue! He adds in an anti-markovnikov fashion, giving more to the guy who has less.
Actually, after typing that out, it's amazing I didn't just confuse the crap out of myself on exams...
"In the end the proud scientist or philosopher who cannot be bothered to make his thought accessible has no choice but to retire to the heights in
which dwell the Great Misunderstood and the Great Ignored, there to rail in Olympic superiority at the folly of mankind." - Reginald Kapp.
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JohnWW
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That would be because B compounds are often electron-deficient, except where polymeric or at least dimeric. BTW Are there any e-books available on
boron or boron-organic chemistry?
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The_Davster
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A while back someone requested "Boronic Acids" by I think Dennis Hall, in the book request thread, but noone ever came up with it. Boron is pretty
cool and Dr. Hall's book sounds pretty interesting.
As with Samosa, hydroboration was one of the earlier reactions I learned in my o-chem course. Interesting way of memorizing it though... ( I had a pretty crazy way to remember the gender on German nouns back when I took
German, not quite that confusing though.)
[Edited on 11-3-2006 by rogue chemist]
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ziqquratu
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A reference that might be of interest to this thread:
Bhanu Prasad et. al., Convenient Methods for the Reduction of Amides, Nitriles, Carboxylic Esters, Acids and Hydroboration of Alkenes Using NaBH4/I2
System. Tetrahedron, 48(22), 1992:4623-4628.
Abstract: Reaction of amides with NaBH4-I2 system in THF gives the corresponding amines in 70-76% yields. Reduction of nitriles yields the
corresponding amines in 70-75% yields. The I2/NaBH4 system is useful in the hydroboration of olefins and the corresponding alcohols are obtained in
78-92% yields after H202/OH- oxidation. The reagent system is also useful for the reduction of carboxylic esters and acids to the corresponding
alcohols in 60-90% yields.
Edit: Got a couple of U2U's saying that they couldnt download this file, so I've upped it to RapidShare as well:
http://rapidshare.de/files/15304956/NaBH4.I2_Reductions.pdf....
[Edited on 12-3-2006 by ziqquratu]
Attachment: NaBH4.I2 Reductions.pdf (390kB)
This file has been downloaded 3186 times
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Sandmeyer
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ziqquratu, that is one hell of a paper, BINGO!
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