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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: emeryx09 on June 01, 2012, 05:11:21 PM

Title: 1- Alkyne + BH3
Post by: emeryx09 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?
Title: Re: 1- Alkyne + BH3
Post by: sjb 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?
Title: Re: 1- Alkyne + BH3
Post by: emeryx09 on June 01, 2012, 08:27:08 PM


Quote
Do boranes react with carbonyls?

I don't quite understand...
Title: Re: 1- Alkyne + BH3
Post by: discodermolide 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?
Title: Re: 1- Alkyne + BH3
Post by: orgopete 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.