Alkenes do not undergo hydration upon treatment with water even at very high temperatures. There are two approaches to hydrating alkenes:
- Reaction of the alkene with water in the presence of a strong-acid catalyst.
- Using an indirect method
Hydroboration-oxidation, sometimes casually called hydroboration for convenience, is a common indirect method used to hydrate alkenes.
The protocol is carried out in two stages:
Stage 1: Hydroboration
The alkene is treated with a source of borane ( diborane or borane-THF complex), which converts the alkene into a trialkylborane.
Stage 2: Oxidation
The trialkylborane is treated with H2O2 and a strong base, usually NaOH, in aqueous medium, which converts the trialkylborane into an alcohol.
This reaction is an anti-Markovnikov addition and a syn addition.
Stage 1 + Stage 2 =
The net reaction is an anti-Markovnikov addition:
see also oxymercuration-reduction