Borane (BH3)
RELATED: 9-BBN, (Sia)2BH
AKA: diborane, B2H6
Most Common Uses
- hydroboration of alkenes and alkynes in hydroboration-oxidation
- reduction of carboxylic acids to primary alcohols
- most common solvent used is THF (tetrahydrofuran)
Hydroboration
FGT: alkene ➛ alkylborane
TYPE: reduction
REGIOCHEM: anti-Markovnikov
STEREOCHEM: syn addition
Hydroborations of alkenes are anti-Markovnikov—BH2 adds to the less-substituted carbon while hydrogen adds to the more-substituted carbon.
It is a syn-addition with the BH2 and H adding to the same side of the alkene.
The alkylborane will react with the alkene two more times to give the trialkylborane. The regioselectivity of each addition improves as the steric bulk of the alkylborane increases.
Reduction of Carboxylic Acids
FGT: carboxylic acid ➛ primary alcohol
TYPE: reduction
REGIOCHEM: n/a
STEREOCHEM: n/a
BH3 can selectively reduce carboxylic acids to primary alcohols.
If LiAlH4 is used, both the ketone and the carboxylic acid are reduced to alcohols.
