Hydroboration-Oxidation

Animated mechanism of the hydroboration-oxidation reaction with propene and BH₃.

1. BH₃ approaches propene in a transition state that induces partial positive charge on the more substituted carbon, leading to anti-Markovnikov regioselectivity.
2. The initial addition forms an alkylborane, which undergoes two more additions to different propene molecules to form a trialkylborane.
3. Peroxide ion attacks the electron-deficient boron center, triggering a 1,2-alkyl migration to relieve the negative charge on boron.
4. Hydroxide ion attacks the boron, followed by expulsion of alkoxide and protonation to yield propanol.