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Also known as: Brown Hydroboration
Discovered by Herbert C. Brown (1959)
A two-step sequence: (1) Hydroboration — BH₃ adds across the alkene with syn stereochemistry and anti-Markovnikov regiochemistry (B goes to less substituted C). (2) Oxidation — H₂O₂/NaOH replaces B with OH with retention of configuration. Nobel Prize 1979.
Hydroboration: BH₃ adds across the alkene in a concerted, syn fashion via a 4-membered transition state. B adds to the less substituted carbon, H to the more substituted.
Concerted, syn, anti-Markovnikov. Repeats 3x (one BH₃ + 3 alkenes)
Oxidation: H₂O₂ in base converts the C-B bond to C-OH with retention of configuration through a 1,2-alkyl migration mechanism.
Retention of configuration — overall syn anti-Markovnikov
1-Hexene
BH₃·THF, then H₂O₂/NaOH
1-Hexanol
1-Methylcyclohexene
BH₃·THF, then H₂O₂/NaOH
trans-2-Methylcyclohexanol
The go-to method for anti-Markovnikov hydration of alkenes. No rearrangements, syn selectivity, and clean regiochemistry make this invaluable.