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Hydroboration/Oxidation
Hydroboration/oxidation reactions reactions:
- occur in multiple steps (first the addition of borane across the alkene followed by oxidation of the carbon-boron bond)
- have anti-Markovnikov addition for a regiochemical outcome (anti-Markovnikov addition has the higher priority group added to the less substituted carbon atom)
- the addition of the OH and H groups is syn (i.e. on the same side) for the stereochemical outcome
Wize Concept
Borane (BH3) exists in nature as a dimer (B2H6), which is unreactive. This is why you will see it as BH3.THF or BH3.Me2S. These are reactive borane species from Lewis acid (boron)/Lewis base (oxygen or sulfur) interactions!
Steps of a hydroboration/oxidation:
- syn addition of the B-H bond across the alkene via a four-membered ring transition state
- oxidation of the B-C bond to form the OH group
Mechanism:
Example: predict the product of the hydroboration/oxidation reaction below.
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Example: Hydroboration
Hydroboration/oxidation reactions can also be used to produce aldehydes from terminal alkynes. Draw a mechanism for the hydroboration/oxidation reaction below.
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Example: Hydroboration
Predict the product(s) of the following hydroboration/oxidation reactions.
