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Topic: 1- Alkyne + BH3  (Read 2977 times)

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Offline emeryx09

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1- Alkyne + BH3
« on: June 01, 2012, 05:11:21 PM »
My textbook say that if 1-alkyne  is added to BH3, then a second addition of BH3 cannot be prevented, therefore diasmylborane should be used. I have trouble understanding why this is. Isn't hydroboration of 1-alkyne similar to hydroboration-oxidation of other alkynes, where it would lead to an enol, which would then form a ketone or an aldehyde, therefore leaving no double bonds which can attack another BH3? How can there be additional reactions with BH3?

Offline sjb

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Re: 1- Alkyne + BH3
« Reply #1 on: June 01, 2012, 06:23:54 PM »
My textbook say that if 1-alkyne  is added to BH3, then a second addition of BH3 cannot be prevented, therefore diasmylborane should be used. I have trouble understanding why this is. Isn't hydroboration of 1-alkyne similar to hydroboration-oxidation of other alkynes, where it would lead to an enol, which would then form a ketone or an aldehyde, therefore leaving no double bonds which can attack another BH3? How can there be additional reactions with BH3?

Do boranes react with carbonyls?

Offline emeryx09

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Re: 1- Alkyne + BH3
« Reply #2 on: June 01, 2012, 08:27:08 PM »


Quote
Do boranes react with carbonyls?

I don't quite understand...

Offline discodermolide

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Re: 1- Alkyne + BH3
« Reply #3 on: June 01, 2012, 09:31:21 PM »


Quote
Do boranes react with carbonyls?

I don't quite understand...


Does BH3 react with aldehydes and ketones?
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Offline orgopete

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Re: 1- Alkyne + BH3
« Reply #4 on: June 04, 2012, 05:13:27 PM »
This is confusing two different reactions. There aren't any carbonyl compounds until step two of the hydroboration (BH3)/oxidation (NaOH, H2O2) reaction. Your textbook is explaining why BH3 isn't used for terminal alkynes. BH3 reacts again with your alkenyl borane. Diasymylborane only has a single hydrogen and I presume less reactive.
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